ABSTRACT Costus spiralis is a Brazilian native plant used in popular medicine, but the safety of this therapeutic use needs investigation. So, the aim of this study was to evaluate the cytogenotoxic and antigenotoxic effects of C. spiralis leaves or stems aqueous extracts on Allium cepa root cells. Moreover, a phytochemical screening and an antioxidant and antifungal activities evaluation were performed. C. spiralis aqueous extracts presented cytotoxicity, but no mutagenicity was observed. When the antigenotoxicity was evaluated, C. spiralis leaves aqueous extract presented preventive and modulatory effects on A. cepa root cells, reducing the sodium azide cytogenotoxic effects. In contrast, C. spiralis stems aqueous extract enhanced the sodium azide cytogenotoxicity in some conditions. The phytochemical screening revealed the presence of phenolic compounds in C. spiralis. When total phenolic content was determined, the leaves presented 73% more phenolic content than stems. Corroborating this data, C. spiralis leaves antioxidant potential was 30% higher than C. spiralis stems. However, these extracts did not present antifungal activity against Candida spp. In conclusion, empirical utilization of C. spiralis aqueous extracts should be avoided. Moreover, the cytotoxic effect of C. spiralis leaves and stems can play an important role in anticancer therapy and must be deeply studied.