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The Northern Tocantins Petrified Forest is classified in the scientific literature as one of the most important Permian assemblages of permineralized plant remains from the warm temperate palaeobiome of the Southern Hemisphere. Part of this forest is located in the Tocantins Fossil Trees Natural Monument, which is a Full Protection Conservation Unit in the northeastern part of the Brazilian state of Tocantins. Geologically, the Petrified Forest is part of the Parnaiba Basin, and the studied stems originate from the Permian Motuca Formation. The aim of the present work is to reconstruct aspects of the regional climate during the Permian by using proxy data obtained from the analysis of gymnospermous fossil stems preserved in the Northern Tocantins Petrified Forest. The material analysed comes from 32 gymnospermous fossil wood fragments derived from nine sampling points located inside and outside the park area. In order to determine climatic influence on wood growth, a total number of 682 growth increments were investigated using mean sensibility and annual sensibility analysis. Moreover, thin sections were made and the anatomical details of the growth patterns of the stems were investigated. The results obtained from these analyses allowed the establishment of the presence of growth zones in the gymnospermous fossil stems. Detailed analysis of these growth zones led to the reconstruction of a seasonal climate with periods of high precipitation alternating with periods of more or less severe dryness, probably in a semi-arid palaeoenvironment. This result is in agreement with previous reconstructions for the Northern Tocantins Petrified Forest area, which postulated a kind of monsoonal climate, characterised by marked seasonality, with strong rains and distinct dry periods.