In severe papulopustular and in nodulocystic/conglobate acne, oral isotretinoin is the treatment of choice. It is also required for patients with moderate to severe acne, especially when acne scars start to occur A new therapeutic approach consists of a low-dose regimen of isotretinoin. We performed a comparative study of high- and low-dose schemas of isotretinoin per os for the treatment of acne. The purpose of this study was to assess the therapeutic effect and tolerability of low doses of isotretinoin in the treatment of acne vulgaris and compare low-dose with high-dose regimens. Sixty-four patients (35 women and 29 men) with different types and grades of acne vulgaris were divided into two treatment groups of 32 patients, in a trial that compared a low dose of 0.15-0.40 mg/kg per day with a high dose of 0.5-1.0 mg/kg per day. These regimens were analyzed with reference to clinical history of acne, baseline investigations, dose and response to isotretinoin, clinical and laboratory adverse effects, relapses and cost of therapy. The mean success rate of the low-dose schema was 69%. The total dose up to 120 mg/kg should be followed for optimal results (success rate of 91%) and avoidance of relapses. The low-dose schema produced fewer adverse effects and offered a very beneficial effect on pre-existing scarring. Our results confirm the beneficial effect of the low-dose schema. We recommend a total dose > or = 120 mg/kg, as this therapeutic regimen of isotretinoin has proven to be the most successful in preventing relapses and scarring.