S E T T I N G : In 2007, the World Health Organization recommended introducing rapid Mycobacterium tuberculosis culture into the diagnostic algorithm of smearnegative pulmonary tuberculosis (TB). O B J E C T IVE : To assess the cost-effectiveness of introducing a rapid non-commercial culture method (thinlayer agar), together with L¨ owenstein-Jensen culture to diagnose smear-negative TB at a district hospital in Kenya. D E S I G N : Outcomes (number of true TB cases treated) were obtained from a prospective study evaluating the effectiveness of a clinical and radiological algorithm (conventional) against the alternative algorithm (conventional plus M. tuberculosis culture) in 380 smearnegative TB suspects. The costs of implementing each algorithm were calculated using a 'micro-costing' or 'ingredient-based' method. We then compared the cost and effectiveness of conventional vs. culture-based algorithms and estimated the incremental cost-effectiveness ratio. RESULT S : The costs of conventional and culture-based algorithms per smear-negative TB suspect were respectively E39.5 and E144. The costs per confirmed and treated TB case were respectively E452 and E913. The culture-based algorithm led to diagnosis and treatment of 27 more cases for an additional cost of E1477 per case. CONCLUSION: Despite the increase in patients started on treatment thanks to culture, the relatively high cost of a culture-based algorithm will make it difficult for resource-limited countries to afford.