All patients with puerperal psychosis admitted to the Royal Edinburgh Hospital within 90 days of childbirth during the periods 1880–90 and 1971–80 were compared. The majority of cases in both groups had an affective illness with an acute presentation and a fixed interval of onset. The 19th-century cases had a more florid presentation and a greater length of admission (mean, 151 days) to the hospital than the 20th-century ones (mean, 39 days). The incidence of the disorder rose from 0.34 per 1000 childbirths per year in the 19th-century group to 1.04 in the 20th-century one, but this could be explained by nosocomial factors. Most 19th-century cases occurred in mulitgravid women, which questions the association of puerperal psychosis with primiparae.