Bleomycin is to treat patients with testicular cancer and lymphoma. Bleomycin can bind to DNA and chelate iron. The resulting complex can form an intermediate capable of interacting with oxygen to produce reactive oxygen species, particularly superoxide. Administrating high-inspired oxygen concentrations (e.g. during anaesthesia or acute illness) has been reported to exacerbate pulmonary injury. The duration of risk after bleomycin chemotherapy is unknown. Here we discuss our advice to a young male patient, who was successfully treated with bleomycin for testicular cancer, concerning the safety to return to scuba diving. Since scuba divers are exposed to high partial oxygen pressures (depending on the depth of the dive) we discouraged this patient from resuming scuba diving.