This article investigates the effect of birth cohort membership on the risk of criminal conviction. The data used are taken from the England andWales Offenders Index and include official conviction histories of six birth cohorts of offenders. Particular problems related to the analysis of official conviction data are discussed, including the need to take account of temporal changes in the age-crime curve caused by social change and criminal policy and the need to be aware of identification issues. A Poisson log-linear model approach is taken. Including data on previous convictions can help explain heterogeneity. An interaction of previous convictions with yearwas found to be important, indicating that additional previous convictions have a greater effect on the conviction rate for more recent years. There is a weak cohort effect for males and a very weak effect for females, after controlling for age, year, previous convictions, and interactions between them.