In many eusocial Hymenoptera, a proportion of males are produced by workers. To assess the effect of male production by workers on the effective population size N-e, a general expression of N-e in Hymenoptera with worker-produced males is derived on the basis of the genetic drift in the frequency of a neutral allele. Stochastic simulation verifies that the obtained expression gives a good prediction of N-e under a wide range of conditions. Numerical computation with the expression indicates that worker reproduction generally reduces N-e. The reduction can be serious in populations with a unity or female-biased breeding sex ratio. Worker reproduction may increase N-e in populations with a male-biased breeding sex ratio, only if each laying worker produce a small number of males and the difference of male progeny number among workers is not large. Worker reproduction could be an important cause of the generally lower genetic variation found in Hymenoptera, through its effect on N-e. Heredity (2012) 109, 261-268; doi:10.1038/hdy.2012.11; published online 5 September 2012