The basic hypothetical relationships underlying Eysenck's theory are that (1) criminals and psychopaths exhibit distinctive personality traits or behavior patterns; (2) there is apparently a genetic basis for these personality traits; and (3) the formation of conscience, which functions to restrain deviant behavior patterns, may be faulty on psychophysiological grounds, resulting in criminal and psychopathic behavior. At the core of Eysenck's theory is the role played by three personality traits: (1) extraversion-introversion, (2) neuroticism, and (3) psychoticism. The bulk of research into the validity of Eysenck's arguments concerns the measurement of these traits in criminal and noncriminal populations. Based on a review of relevant research, the theory falls far short of being an integrated theory of criminality which could be used to guide social practice and intervention. Specifically, the theory does not give needed emphasis or balance to the quality or character of socioeconomic milieus in interaction with individual physiopsychological characteristics, nor does it appreciate that criminal behavior is largely culturally defined rather than being an absolute of an individual's behavior. One note and 40 references are provided.