The objectives of this study were (i) to describe the prevalence of postpartum depression (PPD) in two Norwegian municipalities and (ii) to investigate whether mothers’ age and parity are related to the development of PPD. A total of 2227 women, 437 from M1 and 1790 from M2 participated in the study. Mothers who had given birth between 1 May, 2005 and 31 December, 2006 completed The Edinburgh Postnatal Depression Scale (EPDS) at well baby clinics 6 weeks after delivery. The prevalence of PPD (EPDS ≥ 10) was 10.1%. However, there was a significant difference between the municipalities, with a prevalence of 14.4% in M1 and 9% in M2. Primiparous mothers showed a higher prevalence than multiparous mothers did, and the oldest mothers (36 years and over) showed the highest prevalence. PPD is an issue of importance in Norway, as in many other countries. Public health services should be aware of the higher risk of PPD among primiparous mothers and especially among older primiparous mothers. A small difference in the information provided by nurses to the mothers in the two groups at the home visit 2 weeks postpartum may have produced a significant difference in the prevalence of PPD. The findings may have implications for service delivery in public health.