Objective: to analyze the factors associated to the inconsistent condom use among sex workers. Method: a transversal study, carried out in prostitution area, using the Respondent Drive Sampling. The sample was calculated based on the information by the Sex Workers Association: 600 female sex workers. The study selected seven women with different characteristics regarding color, age, and place of work, who were called seeds. After the participation, they received three coupons to recruit other participants in order to obtain a representative sample. The definition of inconsistent condom use was determined as occasional use or never using it. Univariate analyses and a multivariate logistic regression were performed. Results: 416 female sex workers participated in the study. The associated factors were having studied for less than eight years (Odds Ratio = 27.28), not having a permanent partner (Odds Ratio = 2.79), high alcohol use (Odds Ratio = 5.07), and being black (Odds Ratio = 2.21). Conclusion: the factors associated to inconsistent condom use were: lower education levels, not having a permanent partner, high alcohol use, and being black.