Background: Swimming pool disinfectants and disinfection by-products (DBPs) have been linked to human health effects, including asthma and bladder cancer, but no studies have provided a comprehensive identification of DBPs in the water and related that to mutagenicity. Objectives: We performed a comprehensive identification of DBPs and disinfectant species in waters from public swimming pools in Barcelona, Catalonia, Spain, that disinfect with either chlorine or bromine and we determined the mutagenicity of the waters to compare with the analytical results. Methods: We used gas chromatography/mass spectrometry (GC/MS) to measure trihalomethanes in water, GC with electron capture detection for air, low- and high-resolution GC/MS to comprehensively identify DBPs, photometry to measure disinfectant species (free chlorine, monochloroamine, dichloramine, and trichloramine) in the waters, and an ion chromatography method to measure trichloramine in air. We assessed mutagenicity with the Salmonella mutagenicity assay. Results: We identified > 100 DBPs, including many nitrogen-containing DBPs that were likely formed from nitrogen-containing precursors from human inputs, such as urine, sweat, and skin cells. Many DBPs were new and have not been reported previously in either swimming pool or drinking waters. Bromoform levels were greater in brominated than in chlorinated pool waters, but we also identified many brominated DBPs in the chlorinated waters. The pool waters were mutagenic at levels similar to that of drinking water (~ 1,200 revertants/L-equivalents in strain TA100–S9 mix). Conclusions: This study identified many new DBPs not identified previously in swimming pool or drinking water and found that swimming pool waters are as mutagenic as typical drinking waters.