Sexual offending is on the political agenda but there has been little research focus on the four offence categories—indecent assault against a female, indecent assault against a male, indecency between males and unlawful sexual intercourse with a girl under 16—which together comprise the vast majority of convictions for sexual offences in England and Wales. We consider the criminal record (1963–94 inclusive) of the 6,097 males convicted of one of these offences in 1973. The results are discussed in terms of criminality, heterogeneity, dangerousness and specialization. By recognizing two levels of analysis—general crime level and sex crime level—we argue that sex offenders can be both generalists and specialists; they may range widely across a spectrum of offences but still specialize within sexual offending.