The phenology and ecology of wild cotton, Gossypium hirsutum L., and the boll weevil, Anthonomus grandis Boheman, were studied at two sites along the northeastern coast of the state of Tamaulipas, Mexico, during 1986 and 1987. Wild cotton densities in the region were low and the plant occurred in areas least disturbed by agriculture and human settlements. Peak flowering periods of cotton and weevil densities occurred during fall months. Boll weeevil infestations were relatively low throughout the sample period (7.1% of the total sampled buds and bolls) and never exceeded 31% of the fruiting forms on any sample date. Weevils were active and often reproductive during winter months, but were seldom found during the dry season (March to May) when cotton plants were generally vegetative or leafless. Within the cotton population, boll weevils were aggregated on large plants and often did not infest flowering and fruiting plants close to infested plants. Weevils failed to recolonize the northern study site after the dry season in 1987 although plants flowered and fruited heavily. The possible importance of these wild cotton and weevil populations to cultivated cotton in Mexico and southern Texas is discussed Español