We studied the risk factors for default in isoniazid preventative therapy (IPT) against tuberculosis in 412 people living with HIV (PLWH) in Mae Chan Hospital, Thailand. Default rates decreased from 57% in 1995 to 17% in 1999. Female sex, residence inside Mae Chan District, and registered in the PLWH group at enrollment of IPT were associated with lower default rates. The integration of IPT into the PLWH day care centre activities over the years might contribute to improvements.