Aim The main aim of this article is to compare prevalence and frequency, ages of onset and desistance, and criminal career duration, according to self‐reports and convictions. Method In the Cambridge Study in Delinquent Development, 411 London males have been followed up from age 8 to age 48, in interviews and criminal records. Results Virtually all males admitted at least one of eight offences, compared with about one third who were convicted. In self‐reports, the number of offences was over 30 times greater, the age of onset was earlier and the career duration was longer, compared with convictions. However, the age of desistance was generally later according to convictions. Conclusions Self‐reported ages of desistance may be affected by increasing concealment with age. The gap between the first self‐reported offence and the first conviction provides an opportunity for early intervention. Copyright © 2014 John Wiley & Sons, Ltd.