Cecropia obtusifolia Bertol. (Cecropiaceae) is a tree that grows in secondary vegetation in the tropical rain forest along both coasts of Mexico. Its leaves are used in folk medicine for the treatment of diabetes mellitus type 2. The aim of the present studies was the evaluation of possible genotoxic effects of the aqueous extract from the leaves of Cecropia obtusifolia by means of two different experimental assay models: the wing somatic mutation and recombination test in flies and the micronucleus test from lymphocytes obtained from patients treated with the extract. No toxicity was found to be induced by the leaves of Cecropia obtusifolia. The Drosophila wing somatic mutation and recombination test (SMART) was applied in the standard version with basal biotransformation activity as well as in a variant version with increased cytochrome P450-dependent bioactivation capacity. The ranges of exposure concentrations for these genotoxicity experiments were between 0.82 and 13.32 mg/ml. The extract did not produce any genotoxic effect; however it showed a non significant antigenotoxic effect. The human micronucleus assay in vivo was performed with cultured lymphocytes obtained from six diagnosed type 2 diabetic patients treated daily with 13.5 g of the aqueous extract between 32 and 85 days. No statistically significant increases in cytotoxicity and/or genotoxicity between control and diabetic blood samples were observed.