The details of onset, perceived precipitating factors, associated symptoms, and pain distribution in the painful crisis of homozygous sickle cell (SS) disease have been prospectively recorded in 183 painful crises in 118 patients admitted to a day-care centre in Kingston, Jamaica. Painful crises developed most frequently between 3 p.m. and midnight, most commonly affected patients aged 15-29 years, affected the sexes equally, and were not obviously influenced by menstrual cycle. Of the perceived precipitating factors, skin cooling occurred in 34%, emotional stress in 10%, physical exertion in 7%, and pregnancy in 5% of women of child-bearing age. Cold as a precipitant was not less common in patients with more subcutaneous fat. Pain affected the lumbar spine in 49%, abdomen in 32%, femoral shaft in 30%, and knees in 21%. There was a highly significant excess of bilateral involvement in limb and rib pain. Recurrent painful crises occurred in 40 patients but showed no evidence of involving similar sites on successive occasions. Abdominal painful crises were associated with abdominal distention in 18 (31%) and with referred rib pain in a further 15 (26%) of crises. Fever was common even in apparently uncomplicated painful crises, suggesting that fever is characteristic of the painful crisis itself and not necessarily indicative of infection. Following investigation and treatment in a day-care centre, over 90% of patients returned home.