Freshwater decapods like the palaemonid river shrimp have received little attention in the Baja California Peninsula, México. From the first formal report in 1878 to now, only three Macrobrachium species have been reported (M. americanum, M. digueti, and M. tenellum) from the peninsula in only three basins. We made a taxonomic study of freshwater shrimp, which included an extensive field survey at 81 sites distributed on both the Pacific and the Gulf of California slopes and a revision of material from the area that had been deposited in scientific collections. We report six species of Macrobrachium by adding M. hobbsi, M. michoacanus, and M. olfersii. We also discuss some aspects of the diversity and conservation of these species in the peninsula and provide an identification key for the Macrobrachium shrimp of northwestern México.