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Prevalence studies in psychiatric epidemiology outnumber incidence investigations by a wide margin. This report gives descriptive information about the incidence of depression and anxiety disorders in a general population. Using data gathered in a 16-year follow-up of an adult sample selected as part of the Stirling County Study (Canada), the incidence ofthese types ofdisorders was found to be approximately nine cases per 1,000 persons per year. The data suggest that for every man who became ill for the first time with IntroductionTwenty years ago, Rema Lapouse reviewed the field of psychiatric epidemiology and concluded that the chief task had not been addressed.' Because most studies had focused on prevalence, she found them of dubious worth. "To determine the incidence (emphasis added) of psychiatric disorder, to relate the incidence to environmental and biological characteristics, to use inferences from these relationships as clues to etiology, and thereby to lay the basis for the prevention and control of diseases-these are the tasks of epidemiologic research in mental disorder."' In emphasizing the importance of incidence, Lapouse draws on the distinction between incidence as enumeration of the first occurrences of a disorder over a defined interval of time, and prevalence as a count of all disorders in existence at one time.2'3 Because prevalence rates are influenced by chronic disorders, most of which will have had their origins under circumstances that are remote in time from the period when they are enumerated, she saw prevalence studies as having "no value in uncovering possible etiologic relationships. "' Furthermore, Lapouse and others found many of the prevalence studies inadequate because the rates reported were variable. 4 An exception she noted was the comparability in overall prevalence given by the Midtown Manhattan