Gillnet fisheries in El Golfo de Santa Clara, Sonora and neighboring fishing camps, in the upper Gulf of California, Mexico, were monitored for 114 days, from 23 January to 7 August 1993, and on nine 1-6 day visits from 15 September 1993 to 29 March 1994, to estimate the rate of incidental mortality of the vaquita (Phocoena sinus). Data on fishing effort and vaquita deaths were collected by interviewing fishermen on the beach when they had returned from fishing and by placing observers on different vessels each working day. The deaths of 15 vaquitas were documented during 1993-94. Twelve vaquitas were killed in ca 16,000 hours of fishing effort between January and October 1993: 5 in gillnets (mesh size 10-11cm) set for chano (Micropogonias megalops); 3 in gillnets (‘chinchorro de linea’, mesh size 7cm) for shrimp (Penaeus spp.); 2 in gillnets (mesh size 15cm) for sharks; 1 in a gillnet (mesh size 7.6cm) for mackerel and sierra (Scomberomorus spp.); and 1 in either a gillnet set for chano or for sharks. Two more vaquitas were killed in October 1993 and January 1994 (the last one in a gillnet set for shrimp) and another in a commercial shrimp trawl in February 1993. Most vaquitas were caught in nets set on the bottom; some were caught in driftnets.