A three-stage community survey of a representative group of Southampton mothers was carried out. A semi-structured psychiatric interview was administered at 3, 9 and 15 months post-partum. The results of these interviews are presented and used to assess the extent and timing of psychiatric disorders arising in this period. In contrast to previous studies, it was found that the highest incidence of new cases, variously defined, occurred between the third and ninth month post-partum and not immediately following childbirth. These results are discussed in the context of previous studies using the same definition of caseness.