The decay of the majority of radioactive isotopes involves the emission of gamma ( gamma ) photons with energies of 50keV to 10MeV. Detectors of such hard radiation that are low-cost, highly sensitive and operate at ambient temperatures are desired for numerous applications in defence and medicine, as well as in research. We demonstrate that 0.3-1cm solution-grown single crystals (SCs) of semiconducting hybrid lead halide perovskites (MAPbI sub(3), FAPbI sub(3) and I-treated MAPbBr sub(3), where MA=methylammonium and FA=formamidinium) can serve as solid-state gamma-detecting materials. This possibility arises from a high charge-carrier mobility-lifetime ( mu tau ) product of 1.0-1.810 super(-2)cm super(2)V super(-1), a low dark carrier density of 10 super(9)-10 super(11)cm super(-3) (refs 3,4), a low density of charge traps of 10 super(9)-10 super(10)cm super(-3) (refs 4,5) and a high absorptivity of hard radiation by the lead and iodine atoms. We demonstrate the utility of perovskite detectors for testing the radiopurity of medical radiotracer compounds such as super(18)F-fallypride. Energy-resolved sensing at room temperature is presented using FAPbI sub(3) SCs and an super(241)Am source.