OBJECTIVE To investigate the factors leading to the retreatment for tuberculosis. METHODS Forty-seven retreatment cases with pulmonary tuberculosis, who were discharged from the National Chiba Higashi Hospital from 2000 to 2002. METHODS Data on all retreatment cases were studied as to the condition of the original treatment and factors leading to the retreatment. RESULTS Of the 47 cases, 33 cases received the original treatment in our hospital. Of the 33 cases, 24 cases were relapsed cases and 9 cases were defaulters. Most relapsed cases were male aged 50s and 12 cases (50%) were jobless. As the factors leading to retreatment, the delay in the negative conversion of sputum culture accounted for 11 cases (45.8%) out of 24 cases. No specific factors were found in three cases (12.5%). Among the defaulters, no bias was seen as to age and occupation of cases, but all the cases were male, and they defaulted during the maintenance phase of treatment at the out-patient department. CONSIDERATION: The delay in the negative conversion of sputum culture was the main factor relating to the relapse. Diabetes mellitus (DM) is one of the factors leading to the relapse, but many factors were observed in DM patients. Male cases aged 50s had many factors leading to the relapse. An intensive management for out-patients and involvement of welfare department aiming at the completion of treatment for the socially vulnerable groups might be necessary as the measure to prevent defaulting. CONCLUSIONS The delay in the negative conversion of sputum culture was the main factor leading to relapse, and intensive management for out-patients aiming at the completion of treatment is necessary to prevent the defaulting.