In this study, morphological characters were used to describe the diversity and seasonal variability of the genus Pseudo-nitzschia in a coastal region of the Mexican tropical Pacific Ocean. Eleven species were characterized from cultures and field material: Pseudo-nitzschia americana , Pseudo-nitzschia australis , Pseudo-nitzschia brasiliana , Pseudo-nitzschia delicatissima , Pseudo-nitzschia cf. delicatissima , Pseudo-nitzschia dolorosa , Pseudo-nitzschia cf. fryxelliana , Pseudo-nitzschia micropora , Pseudo-nitzschia multistriata , Pseudo-nitzschia pungens var. aveirensis , and Pseudo-nitzschia subfraudulenta. The maximum diversity and abundance occurred in spring, in parallel with a local upwelling, whereas fewer species were detected in autumn. Among those analyzed, the only species to be detected throughout the year at several stations was P. cf. fryxelliana , whereas the rarest species in the study area was P. americana , which was detected only in the spring.