Objectives: To establish modifiable factors associated with active pulmonary tuberculosis (PTB) among prisoners. Design: Retrospective matched case-control study. Setting: Nakuru GK prison in Kenya. Subjects: A total of l44 subjects (48 cases and 96 controls) were recruited into the study.Cases were adult prisoners who had at least two initial sputum specimens being Acid Fast Bacilli-positive (AFB+) on direct smear microscopy and hence recruited to PTB WHO DOTS Programme. Controls were adults with no chronic cough and not on PTB treatment six months prior to the study. Results: Independent factors significantly associated with active PTB disease were:self reported HIV+ status (OR=11; 95%CI = 2.42-47.77), evidence of BCG vaccination (OR = 0.20; 95%CI = 0.05-0.60), contact with PTB case (OR = 7.0; 95%CI =1.17-38.23), unemployment (OR = 9.0; 95%CI = 1.84-43.97) and sharing linen (OR = 4.32; 95%CI = 1.08-17.29). Conclusions: Modifiable factors associated with active PTB in Nakuru G.K prison are:HIV status, BCG vaccination, PTB case contact, poverty and poor personal hygiene. We recommend HIV counseling and testing of all PTB patients, screening for TB upon prison entry and TB contact investigation and improving personal hygiene of persons