-The purpose of this paper, which was conducted on 175 children with hemiparetic cerebral palsy (H-CP), was to verify the etiological risk period for this disease. Etiological risk factors (ERF) were detected through anamnesis: 23% in the prenatal period, 18% in the perinatal period and 59% of the patients the period was undefined (ERF in the prenatal and perinatal period was 41% and no ERF was 18% of the cases. The computerized tomographic scan (CT) and MRI were performed on all the patients, who were then classified according to their etiopathogenic data: CT1= normal (18%); CT 2= unilateral ventricular enlargement (25%); CT 3= cortical/ subcortical cavities (28%); CT4= hemispheric atrophy and other findings (14%); CT 5= malformations (15%). CT 5 was associated with physical malformations beyond the central nervous system and with prenatal ERF s , while CT 2 was associated with the perinatal ERF s, mainly in premature births. Magnetic resonance imaging was performed on 57 patients and demonstrated a good degree of concordance with the CT. Etiology remained undefined in only 37% of the cases after neuroimaging was related to ERF. A high perinatal RF frequency (59%) was observed and emphasized the need for special care during this period.KEY WORDS: cerebral palsy, hemiparetic cerebral palsy, etiology, etiological risk factors, computerized tomography, magnetic resonance imaging, children.Paralisia cerebral hemiparética: fatores de risco etiológico e neuroimagem RESUMO Foram estudadas 175 crianças com paralisia cerebral hemiparética (PC-H) para elucidar o período de risco etiológico. Através da anamnese constataram-se fatores de risco para etiologia (FRE) pré-natal em 23%, perinatal em18% e período indefinido em 59% dos pacientes (com FRE pré e perinatal 41% e sem FRE 18%). A tomografia computadorizada (TC) foi realizada em todos os sujeitos e classificada de acordo com dados etiopatogênicos em: TC1= normal (18%); TC2= alargamento ventricular unilateral (25%); TC3= cavidades córtico-subcorticais (28%); TC4= atrofia hemisférica e outros achados (14%); TC5= malformações (15%). A TC5 se associada a malformações físicas fora do sistema nervoso central e aos FRE pré-natais e a TC2 aos perinatais, principalmente, nascer prematuro. A ressonância magnética foi realizada em 57 sujeitos demonstrando boa concordância com a TC. Após associação da neuroimagem e FRE a etiologia ficou indefinida em apenas 37%. Constatou-se alta frequência de FRE perinatais (59%), alertando para melhores cuidados neste período. PALAVRAS-CHAVE: paralisia cerebral, paralisia cerebral hemiparética, etiologia, fatores de risco, tomografia axial computadorizada, ressonância magnética, crianças Despite the recent improvement in maternal infantile health care, cerebral palsy (CP) and its mechanisms are still not fully understood. The incidence of this disease, in its moderate and serious forms is around 2.5:1000 live births 1 . CP is defined as a non progressive motor disorder which is secondary to a lesion of an immature brain and includes abn...