context: pharmacovigilance studies aim to detect, assess, understand and prevent risks of adverse effects of medications or any other possible drug related problem. alpha interferon is being produced by bio-manguinhos/fiocruz, rio de janeiro, rj, brazil and used in the treatment of chronic hepatitis c at brazilian national health system. objective: to study the safety profile and effectiveness of alpha interferon in a sample of brazilian patients with chronic hepatitis c genotypes 2 and 3, in porto alegre, rs, brazil. method: we followed a cohort of chronic hepatitis c genotypes 2 and 3 patients treated with alpha interferon plus ribavirin in a specialized outpatient clinic in southern brazil. adverse events were collected and classified according to severity in monthly structured interviews. to measure effectiveness, hepatitis c viral load was evaluated before, at the end and 24 weeks after the treatment. results: we followed 141 patients during the study period, of which 52.5% were female with mean age of 52 years. the most frequent adverse events were fatigue (84%), headache (79%) and myalgia (75%). there were 13 treatment interruptions due to adverse events, 9 of those considered serious adverse events. virological response at end of treatment was 54.6% and after 24 weeks 39.7%, considering all patients who started treatment. conclusion: the product produced by bio-manguinhos has similar efficacy and adverse event and sustained virological response profiles comparable to those found in the literature. this is the first study of pharmacovigilance performed with the brazilian product. these data will be useful for planning and management of this disease in brazil.