The relationship between bone pain and stress fractures diagnosed by bone scintigraphy was investigated in military recruits during active training. In three patients pain appeared in the site of abnormal uptake 7-14 days after the bone scan in a previously asymptomatic site. One hundred and twenty-four sites of stress fractures were found in 64 patients; 32 (26 per cent) were asymptomatic. In 38 patients (59 per cent) there were multiple stress fractures; 32 (33 per cent) had asymptomatic stress fractures. Fifty-three per cent of the regions with abnormal uptake in the femur were painless, compared with 17 per cent in the tibia. The necessity for imaging all bones susceptible to stress fractures, even when asymptomatic, is stressed. It is suggested that diagnosis of stress fracture should be made when typical abnormal uptake appears on scintigraphy. Bone pain in such cases may be delayed.