The purpose of the present paper is to investigate the usefulness of routine notification of antituberculosis drug susceptibilities. In Switzerland, laboratories have to report susceptibilities to isoniazid, rifampicin, ethambutol, and pyrazinamide to the Federal Office of Public Health. All clinical and laboratory information on every single tuberculosis case is routinely linked. Proportions of drug resistance were calculated and logistic regression was applied to evaluate the role of potential risk factors. Eighty percent (1056) of all culture-positive tuberculosis cases reported between October 1995 and December 1997 were analysed. The strains of 66 (6.3%) patients had resistances to at least one drug. Risk factors identified were previous antituberculosis treatment (adjusted odds ratio 7.3, 95% confidence interval 3.9-13.6), male sex (1.4, 1.1-2.0), and age <65 yrs (1.5, 1.0-2.3). Fourteen cases (1.3%), 13 of them foreign-born, were resistant to at least isoniazid and rifampicin. Reporting of drug susceptibilities allows routine assessment of the proportion of drug resistant tuberculosis and populations at risk. This proportion was found to be small in Switzerland. Risk factors were previous treatment for tuberculosis, male sex, and age <65 yrs. Resistance to at least isoniazid and rifampicin was predominantly found in foreign-born patients.