One thousand and forty people aged 40 years and over, 616 (59.2%) of whom had solar keratoses, were followed for 12 months. Two hundred and twenty-four people (36.4%) had a spontaneous remission of at least one of their solar keratoses. A total of 485 lesions (25.9%) underwent spontaneous remission out of the 1873 lesions that were present at the first examination of these 224 people. There was no significant difference between the number of lesions present at the initial examination in those who had a spontaneous remission compared with those who did not. There was a 21.8% increase in the total number of solar keratoses in the 1040 people studied in the 12-month period, due to new lesions forming at the same time as remissions were occurring. The incidence rate of squamous cell carcinoma occurring in the people with solar keratoses was 0.24% for each solar keratosis present at the original examination. With a substantial proportion of solar keratoses remitting spontaneously, plus the low rate of malignant transformation and the low potential for metastasis to occur from squamous cell carcinoma arising in a solar keratosis, the rationale of treating all solar keratoses appears questionable.