15 out of 40 women on a post natal ward had headaches in the first post partum week, particularly between day 3–6 post partum. The incidence of these headaches was increased among women with a previous personal or family history of migraine or pre-menstrual migraine, but they were usually milder and more frequently bilateral than the patients usual migraine. These headaches were not associated with previous neurotic depression or mood changes during the puerperium and are therefore unlikely to be tension headaches. Weight gain preceded the onset of the headache and weight loss followed it, but as these changes occur among women without the headache they are unlikely to be causal, though of interest since similar weight changes sometimes occur with migraine attacks. The rapidly falling levels of estrogen and progesterone, or possibly alterations in serotonin metabolism may be responsible for these headaches, most of which appeared to be mild episodes of common migraine.