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We analyzed the influence of mean annual rainfall and duration of seasonal drought on soil P cycling along a rainfall regime gradient including mature tropical dry forests growing under similar temperature, rainfall seasonality and geological (limestone) conditions. We investigated the distribution of different P forms in fine roots, litterfall, forest floor and mineral soils, and we examined how the distribution was related to rainfall regime. The total concentration of extractable P differed across sites. Thus, the P concentration in roots and litterfall was higher in the wettest stands than in the driest stands. The P concentration fluctuated in the forest floor, and in mineral soils it increased as the rainfall decreased. Solution P-31 NMR revealed that orthophosphates and monoester-P dominated the P content of roots, litterfall, forest floor and mineral soils. Although the concentration of orthophosphate in roots decreased as the rainfall decreased, this P form accumulated in the forest floor and mineral soils under conditions of drought. Low rainfall also affected the concentration of monoester-P in roots, litterfall and mineral soils, which decreased as rainfall decreased. Diester-P and pyrophosphate were detected in small amounts in all materials analyzed, and although the concentrations of these compounds in roots fluctuated across the rainfall gradient, they generally decreased in the litterfall and mineral soils with decrease in rainfall. We conclude that the long-term consequences of an increase in drought in these forest ecosystems will include a decrease in the cycling of organic P forms and an increase in inorganic P content in soils, mainly due to restricted uptake of P by plants and less soil leaching. If primary productivity is maintained, these tropical dry forests may therefore become significant soil P hotspots under the predicted increased duration of drought.