Ob jec tive: To re view pub lished works on the epi de mi ol ogy, risk fac tors, pro tec tive fac tors, ty polo gies, and ge netic as pects of conduct dis or der (CD). Method: Find ings from refe reed jour nal ar ti cles and cur rent texts in the field are briefly sum ma rized.For our dis cus sion is on no tri fling mat ter, but on the right way to con duct our lives. Plato, The Re pub licT his ar ti cle sum ma rizes rele vant find ings on epi de mi ology, en vi ron mental con tri bu tions, sub types, and ge netic as pects of CD. Other im por tant as pects, such as as sess ment, comor bidi ties, neu rop sy chi at ric vul ner abili ties, and treatment have been re cently well-reviewed (1-3). This pa per updates the reader on cur rent think ing about psy cho so cial risk and pro tec tive fac tors and hints at emerg ing bio logi cal risk fac tors, such as ge net ics. We con sulted origi nal ar ti cles and re views in both Med line and Psycinfo, par ticu larly those published over the last 15 years. For fur ther in for ma tion, please con sult the origi nal ref er enced works. Clini cal and pub lic health im pli ca tions are in di cated, where ap pro pri ate. DefinitionsCD is 1 of 3 dis rup tive be hav iour dis or ders (4), the oth ers being op po si tional de fi ant dis or der (ODD) and attention-deficit hy per ac tiv ity dis or der (ADHD). As in di cated in the DSM-IV, CD con notes a se vere ex ter nal iz ing dis or der com pris ing se rious ag gres sive and an ti so cial be hav iours such as fight ing, bul ly ing, cru elty, rob bery, forc ing sex ual ac tiv ity, fire set ting, theft, con ning, tru ancy, and other rule vio la tions. An ti so cial be hav iour de scribes ac tions con trary to the rights of oth ers and rules of so ci ety. Ado les cent an ti so cial be hav iour that breaks the law (and gets caught) may re sult in con tact with po lice and the courts; the terms "de lin quent" and "young offender48 would then ap ply. Thus, CD rep re sents a con stel lation of an ti so cial be hav iours; a sub group of youths with se vere CD will be de lin quents (5). We will also use the terms "ag gres sion" and "vio lence" in this over view. Ag gres sion is de fined as out ward de struc tive be hav iour that re sults from the con flu ence of longer-term fac tors (for ex am ple, bio logi cal, psy cho logi cal and per son al ity, fam ily, peer, school, and commu nity), short-term in flu ences (for ex am ple, in ter nal states of an ger, bore dom, or in toxi ca tion) and situa tional op por tu nity. Vio lence-a par ticu lar form of overt and in ten tional ag gression-uses or credi bly threat ens to use physi cal force such as beat ing, kick ing, chok ing, us ing a weapon, forc ing sex, and throw ing ob jects.

Specu la tion about the physi cal and neu roa na tomi cal aspects of crimi nal be hav iour be gan with Franz Jo seph Gall at the end of the 18th cen tury. His ob ser va tions evolved into phre nol ogy, a the ory that as signs spe cific men tal func tions to to pog raphi cal re gions of the skull (1). Un til re cently, EEG was one of our main meth ods of look ing at brain ab nor malities in cases of ag gres sive be hav iour, but the non spe cific and rela tively un lo cal ized na ture of the find ings lim ited its in terpre ta tion. Now, more than 2 cen tu ries af ter Gall, neu roi maging tech nolo gies prom ise to greatly en hance our un der stand ing of the bio logi cal un der pin nings and sub strates of an ti so cial be hav iour in a way that Gall could not even imag ine. Struc tural tech niques, such as CT or mag netic resonance im ag ing (MRI), look at brain ar chi tec ture, de tail ing size, shape, and lo ca tion of tis sue dam age. Func tional approaches, such as posi tron emis sion to mo gra phy (PET) or func tional MRI, add the di men sion of live neu ral ac tiv ity. This pa per re views im ag ing tech nol ogy as ap plied to the study of an ti so cial be hav iour. Each ap proach is sum ma rized and fol lowed by rele vant clini cal stud ies. For a more de tailed dis cus sion of the tech ni cal as pects of neu roi mag ing as sessment, the reader is re ferred else where (2,3).The ear li est im ag ing method in volved X-rays, dis cov ered in 1895. A form of elec tro mag netic ra dia tion, X-rays pro vide con trast as they at tenu ate dif fer ently, de pend ing on tis sue den sity. The soft tis sues of the brain proved to be a bar rier to use, how ever, ex cept for gross pa thol ogy due to brain displace ment. In 1918, the next de vel op ment was pneu moencepha lo gra phy (4). Here, air was in jected into the subarach noid space, fol lowed by de linea tion of ven tri cles. In 1927, an emerg ing func tional tech nique, cere bral ar te ri og raphy, was de vel oped (5). The next mile stone was Wa da's injec tions of so dium amy tal into the ca rotid ar tery to as sess lan guage lat er al ity (6). The pre-CT era was largely domi nated by an gi ogra phy. Com put er ized To mo gra phy (CT)To mo graphic im ag ing re fers to X-ray im ages of spe cific planes within the body. The digi tal com puter revo lu tion of the late 1960s made CT pos si ble. Also known as com put er ized ax ial to mo gra phy (CAT), CT was de vel oped in the early 1970s by God frey Houns field of Great Brit ain and Al len Cormack of the US. Nar row beams of X-rays sweep se quen tially across the head, re sult ing in a se ries of elec tri cal im pulses recorded by a ra dia tion de tec tor. So phis ti cated com puter software in te grates the data, us ing the ra dia tion ab sorp tion

Clinicians can use findings from reviewed controlled and, where necessary, uncontrolled studies to inform pharmacologic practice. This review offers suggestions for future research directions that will aid clinical practice.