To determine the incidence of relapse in patients with lung tuberculosis and its associated risk factors. A follow up study was conducted with 237 patients who were cured after receiving treatment in rural medical facilities from the State of Chiapas. The global incidence of relapse was 1.04 cases per 100 month/person. The risk factors for relapse were lack of knowledge about treatment (OR = 2.28; 95% CI = 1.06-4.89); drug adverse effects (OR = 2.78; 95% CI = 1.31-5.90), waiting time for more than 15 minutes to receive medical care (OR = 3.07; 95% CI = 1.06-12.94) and lack of medical supervision (OR = 4.77; 95% CI = 1.30-17.41). Most of the risk factors for relapse are susceptible to modification and are related with the quality of medical care provided to lung tuberculosis patients.