Objective: To investigate the use of the plant Sphagneticola trilobata by farmers as an adjunct in the treatment of diabetes mellitus.Method: We interviewed five farmers with diabetes mellitus and who used S. trilobata, in Rio Grande, Rio Grande do Sul in the period from June to July 2009.The study was approved by the Ethics and Research of the Faculty of Medicine, Universidade Federal de Pelotas (072/07).Results: All respondents were female aged between 48 and 74.The leaves were the most used.The tea is prepared by infusing the plant.The knowledge of insulin has been passed on by relatives or neighbors.The interviewees reported hypoglycemic effect after use of the plant.Conclusion: The popular knowledge about medicinal plants is usually passed on through family generations, and its front of complementary therapies in this way meets the needs of the individual, complete health services.