The prevalence of drug resistance to Mycobacterium tuberculosis complex (MTBC) shows marked geographic difference and is the key to determining drugs of choice for the initial treatment of tuberculosis (TB). This retrospective study investigated the MTBC resistance rate and its contributing factors based on the review of medical records from a hospital in central Taiwan. TB culture and antimicrobial susceptibility test were performed using the BACTEC MGIT 960 System. Isoniazid, rifampin, ethambutol and streptomycin were tested. Molecular detection of MTBC using BDProbeTec ET kits was conducted in positive culture media containing acid-fast bacilli. Between July 2001 and June 2002, 974 (12.4%) strains of MTBC were isolated from 7892 clinical specimens from 513 patients. They included 348 males and 165 females with mean age of 66.1 +/- 15.6 years and 63.4 +/- 19.2 years, respectively. Sixty one percent of patients were older than 64 years of age. The overall resistance rate to 1 or more drugs was 22.4% (n = 115). The number of strains resistant to individual drugs was 86 (16.8%) to isoniazid, 25 (4.9%) to rifampin, 21 (4.1%) to ethambutol, and 63 (12.3%) to streptomycin. Twenty (3.9%) isolates were resistant to at least isoniazid and rifampin. A history of anti-TB treatment was associated with drug resistance (36.8% vs 20.6%, p=0.0056). Only 22 (4.3%) patients were tested for HIV antibodies and the results were all negative. The prevalence of resistance to anti-TB drugs remains high in Taiwan and is associated with a previous history of anti-TB treatment. Retreatment may contribute to an increased prevalence of multiple drug resistance.