Abstract. The objective of this study was to observe the prevalence of drug resistance in Mycobacterium tuberculosis isolates in HIV associated tuberculosis co-infected patients in Phnom Penh City. The isolates of M. tuberculosis were collected during active laboratory-based surveillance. Of the 98 isolates studied, M. tuberculosis resistance to isoniazid was seen in 23.5%, resistance to rifampicin was seen in 16.3% and multidrugresistance (MDR-TB) was seen in 5.1%. Our findings reveal an alarmingly high level of resistance to isoniazid and rifampicin, and confirms the need for drug susceptibility
testing to guide treatment in patients with culture positive tuberculosis.