Ninety-one patients admitted to a geriatric unit with apparently undamaged sacral akin were examined by thermography. Nineteen per cent showed a thermal pattern consistent with occult skin damage, and 35% of these developed an overt pressure sore at the thermographically abnormal site within 10 days of admission. None of the remaining patients developed a sore within this time. Thermography can provide a more precise indication of the risk of early development of a sacral pressure sore than the Norton score.