To access this article, click on "Additional Links".We conducted a study among patients with tuberculosis (TB) attending two health facilities - a hospital and a slum health centre - in Nairobi, in order to: (a) assess adherence to anti-TB treatment; and (b) identify reasons for non-adherence. Urine Isoniazid (INH), used as a proxy for overall adherence, was detected in 142 (97%) (95% CI 92-99) of the 147 patients involved in the study. Five patients had no INH detected in urine and had run out of pills within the previous three days. The reasons included: not having enough pills to last until the next appointment date (1); and losing some pills (1). Anti-TB treatment adherence is high, and is reassuring information as Kenya plans to change to a superior first-line regimen based on rifampicin throughout the course of anti-TB treatment. Providing patients with a three-day "excess stock" of pills would provide a "safety net" for continued treatment.