BACKGROUND: Acne is a chronic inflammatory disease of the pilosebaceous unit, characterized by the formation of comedone, erythematous papules and pustules, psudocysts or nodules and is accompanied by scarring in severe case. Although vitamin A derivatives have known to be effective on acne lesions, but there are still controversy on the therapeutic efficacy and patient's compliance. OBJECTIVE: This study was performed to evaluate the therpeutic effect and side effects of oral isotretinoin(RoaccutaneR) for acne patients. METHOD: Thirty three patients with moderate to severe degree acne enrolled in this study. Oral isotretinoin was intentionally given at 20-60mg daily according to the clinical severity for 4 month duration. For clinical evaluation, papule(<4mm in diameter) and nodule(>4mm) of acne were counted in the selected area. Degree of erythema and rate of involved area of acne lesion were scored from 1 to 4. and from 0 to 8 individually. They was checked at 0, 2, 4, 6, 12, 16 week and 4week and 8week after therapy. Side effects and renal function test, liver function test, and serum lipid level were also evaluated. Clinical improvement was statistically evaluated according to median dosing level, which were two groups of daily 0.2-0.5mg/kg and 0.5-1.0mg/kg. RESULT: The patients were 16(48.5%) who revealed more than 90% of reducing at all clinical lesions and scores. and 26(78.8%) who more than 70%. However, there was no statistical significance between 0.2-0.5mg/kg/day group and 0.5-1.0mg/kg/day group. The clinical responses are more rapid on the papules, pustuls, and nodules than erythema and percent of involved area. Side effects were observed at 24 patients(69%), which were more in 0.5-1.0mg/kg/day group than 0.2-0.5mg/kg/day group, such as cheilitis, facial dermatitis, gastric discomfort, xerosis, nasal bleeding, oral xerosis, and urethritis. But they were not much severe disturbing the treatment. CONCLUSION: This study suggest that the oral isotretinoin (RoaccutaneR) therapy is effective and relatively safe for moderate to severe acne. In addition, small doses of oral isotretinoin, 0.5mg/kg/day, also considered to be as effective as higher doses.