Twenty five patients with severe and extensive psoriasis were treated with trimethylpsoralen (trioxsalen) bath plus ultraviolet A (bath PUVA) combined with oral retinoid, etretinate (Ro 10-9359). Etretinate was started (1 mg/kg/day) 2 weeks prior to starting the bath PUVA treatment daily. Psoriasis cleared with fifteen treatments in 96% of patients with a mean total UVA dose of 3.9 joules/cm2. The control group of nine patients received only bath PUVA without retinoid, and eight of them cleared with nineteen treatments and with a mean UVA dose of 7.2 joules/cm2. In addition, three psoriatic patients previously resistant to bath PUVA treatment were given etretinate (1 mg/kg/day), and they cleared in 4 to 8 weeks after starting etretinate with a UVA dose of 37-144 joules/cm2. In the maintenance therapy after the combination therapy of twenty-four patients, the results of treatment were good or excellent in fourteen of fifteen patients (93%) getting only bath PUVA one to two times a week and in four of nine patients (44%) getting etretinate (25-50 mg daily) in a mean follow-up time of 10 weeks. These results show the benefits of the combination of trimethylpsoralen bath PUVA with an oral retinoid, etretinate, in the treatment of severe and extensive psoriasis.