INTRODUCTION This case report of benign summer light eruption emphasizes the importance of phototests in the diagnosis of photosensitive dermatoses. METHODS A 25-year-old man, phototype II, had experienced a pruriginous papulovesicular erythematous eruption of the axillary and inguinal regions each summer for 12 years. A high-dose UV phototest (40 J/cm2 x 3 days) directed on the right posterior axillary area and a whole body exposure test (4 J/cm2 UVA, 20 mJ/cm2 UVB x 3 days) were positive both clinically and histologically on day 4. DEM B was normal at 26 mJ/cm2. Iterative polychromatic phototest (DEM x 3 days) in the area usually involved (left posterior axillary region) was negative. The simple UVA (13 J/cm2) and iterative phototests performed on the back were negative. The results of the phototests led to the diagnosis of benign light eruption despite the unusual localization. CONCLUSIONS The diagnosis of benign light eruption is generally clinical. Phototests are unnecessary in most cases. Benign light eruption can be triggered by high-dose iterative UVA exposure of the susceptible area or whole body phototests (UVA-UVB). These specific phototests are indicated in atypical forms or localizations in order to determine the course of benign light eruption and to uncover simulations.