Among the 13 individuals with recorded convictions only after age 22, there was evidence of at least minor juvenile delinquency in every case but one. There was major adult mental illness whose onset preceded the first conviction in four cases. Levels of childhood antisocial behaviors were significantly higher among this group compared with those who had never been convicted; and levels of major mental illness were significantly higher compared with those who had never been convicted and those with convictions only up to age 21. Apparent late onset criminality in the study sample was therefore associated with known risk factors for adult criminality, namely, juvenile antisocial behavior and/or major mental illness. The researchers conclude that it is unlikely there is a single "correct" explanation for criminality that begins in adult life. The factors associated with this offending pattern probably vary from sample to sample. In general-population or low-risk samples, there may be larger numbers of individuals whose criminality was not preceded by antisocial behavior in childhood or associated with psychiatric disorder in adult life. For such individuals, social factors of the kind described by Sampson and Laub (1993), such as the loosening of informal social controls through weakened ties to the family or work, may have a more important role in the onset of criminality. Future strategies for the study of individuals with a late onset of criminal behavior might begin by identifying those without a history of mental illness or childhood disturbance. 2 tables and 30 references