Postnatal depression (PND) affects about 10-15% of women and can last more than a year in chronic cases. The Edinburgh Postnatal Depression Scale (EPDS) is a well-known questionnaire for screening PND symptomatology during the first weeks after birth, but its use in later periods is rare, reflecting a tendency to pay more attention to the onset of PND instead of its course. The study aimed to explore stability of PND symptomatology at 3, 9 and 18 months after birth, using the EPDS. Depression rate decreased from 3 to 18 months postpartum. Onset of symptoms was mainly within the first 3 months; 23.4% of 167 women showed an EPDS score > or =13 on at least one of the assessments, and 7.2% of women did so on at least two assessments. Over the 18-month period, the number of women who had recovered in the period from one assessment to the following was not significantly different from the number of women becoming depressed. Our findings underline the need to consider the existence of different courses of depressive symptomatology in research and clinical practice; women with persistent or recurrent depressive symptoms need forms of preventive intervention that cover at least the first postpartum year.