Five hundred and sixty-three primary cutaneous melanomas were assessed for the presence of histological regression in relation to the thickness of the lesion and features such as sex, anatomical location and clinical outcome. Regression was more common in thin lesions, being seen in 46% of thin (less than 1.5 mm) lesions, 32% of intermediate (1.5-3.0 mm) lesions and 9% of thick (greater than 3.0 mm) lesions. However, severe regression was only identified in 6.5% of thin lesions, 5.2% of intermediate lesions and 1.5% of thick melanomas. Regression was more common in superficial spreading melanomas and in lesions from the trunk and lower limb. Moderate and severe regression were seen slightly more often in men. Clinical follow-up, although not of statistical significance, suggests that regression in thin lesions is a sinister histological feature.