We report the results of a French multicentre study to evaluate the efficiency of psoralen plus ultraviolet A (PUVA) therapy in the prophylactic treatment of benign summer light eruption (BSLE) and to establish the optimal protocol of radiation. Nine photobiology centres took part in this study; 83 patients (76 of them women) were evaluated. The radiation protocols were as follows: oral psoralen (8-methoxypsoralen; 0.6 mg/kg) was taken at each session; the starting dose of UVA radiation was determined according to skin type, with increments of 0.5 J/cm2 every 2 sessions. The subjects were randomized to receive 10-20 sessions 3 times per week. PUVA therapy was very effective: 68 patients (82%) reported total protection from BSLE. Four patients (5%) showed progress. Only 13% showed no improvement. The satisfactory results were not correlated with either the number of sessions or the J/cm2 of UVA. The intensity of tanning after the PUVA sessions did not appear to predict cure. Thirty-six percent of the patients had adverse reactions to treatment, including erythema, pruritus and triggering of BSLE. However, these effects only required the treatment to be stopped in 2% of the cases (for severe pruritus). The results in the various centres were similar.