We examined the spatial and temporal abundance as well as some biological features of the four Pleuronectidae species living in the shallow and deep marine waters off the western coast of Baja California: spotted turbot Pleuronichthys ritteri (Starks & Morris, 1907); hornyhead turbot Pleuronichthys verticalis (Jordan & Gilbert, 1880); slender sole Lyopsetta exilis (Jordan & Gilbert, 1880), and Dover sole Microstomus pacificus (Lockington, 1879). Flatfishes were sampled by otter trawls during six cruises, between October 1988 and September 1990. The area sampled covers three geographic regions (Southern, Central and Northern) and three depths (inner, middle and outer shelf). The data were analyzed to quantify the ecological variation in environmental factors and spatial assemblages. Spatial patterns of the Pleuronectidae assemblages were determined by depth, sediment type and geographical region. The distribution of Pleuronectidae species across the shelf also varies in time depending on the oceanic regimes. The sex ratio was approximately 1:1 for all four species. Standard length ranged from 45 to 261 mm, with the most frequent sizes ranging from 90 to 130 mm. For turbots, the length-weight relationships varied between sexes, geographical regions and seasons of the year.