The aim of this study was to examine the prevalence of vasectomy and associated factors in New Zealand, based on interviews with men. Participants were randomly selected from European men, aged between 40 and 74 years, on the general electoral roll. Telephone interviews were completed with 1225 men between 1997 and 1999. Overall, the prevalence of vasectomy was 44% (95% CI, 37-52%), adjusted to the age distribution of all New Zealand men aged 40-74 years. The prevalence ranged from 57% of men aged 40-49 years to 15% of those aged 70-74 years. Catholic men had a significantly lower odds of vasectomy, and there was a trend in increasing odds of vasectomy with increasing number of marriages and level of education of the wife. The results confirm a very high prevalence of vasectomy among New Zealand men. Comparison with earlier surveys based on interviews of women showed an increasing prevalence of vasectomy in each birth cohort from the 1920s to the 1950s. Vasectomy has been popular with men across all socioeconomic groups. New Zealand is an ideal country in which to study consequences of vasectomy.