Ciprofloxacin is a broad spectum quinolone antibiotic. Side effects reported include nausea and other gastrointestinal symptoms; skin and musculoskeletal side effects may also occur. No bleeding abnormalities or alteration in coagulation have been documented. We report a case where ciprofloxacin appeared to contribute to an idiosyncratic prolongation of bleeding time although a rechallenge 8 months later did not reproduce the effect. Moreover, subsequent investigation of the influence of ciprofloxacin on bleeding parameters in 10 healthy volunteers demonstrated no alterations in bleeding parameters.