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The Pilosocereus pachycladus F. Ritter is a native cactus, which grows in the semi-arid area of northeastern Brazil. They have an ornamental value, yet studies on their ecology are scarce. The species is sensitive to human disturbance due to the low absolute growth rate, the restricted geographic distribution and the dependence of dispersal agents. We analyzed the population structure of P. pachycladus in disturbed caatingas areas in the Westland of Paraiba. Structural surveys were made in the municipalities of Areial and Boa Vista, PB. We sampled all individuals and measured the height and diameter of each plant in a 1-ha area. The Surfer (R) application was used to predict the spatial distribution of this species. In the Areial, 179 adults and 91 in natural regeneration (Absolute density, AD = 270 ind/ha) were sampled; while in the Boa Vista 169 in adulthood and 3 in natural regeneration (AD = 172 ind/ha) were found. The population of P. pachycladus in Areial showed a lower basal area (BA = 2.10 m(2)) compared with the population of Boa Vista (BA = 3.82 m(2)). In both caatingas individuals tended to cluster. It seemed that the populations were spatially present in small clusters within the studied environments. The specimens of Areial, area where a higher degree of human disturbance was observed, had a lower stem diameter and total height, in comparison to Boa Vista, PB, which is a more conserved land area. The populations showed similarity in terms of spatial distribution, yet structurally the anthropization affects significantly the development of P. pachycladus.