A survey of the crystal structures of pyrazoles reported in the Cambridge Structural Database has been analyzed using the diagrams of Dieterich. (D.A. Dieterich, I.C. Paul and D.Y. Curtin, J. Am. Chem. Soc., 96 (1974) 6372). Structures have been classified according to the substituent at position 1 of the pyrazole ring. A total of 209 data were analyzed. For eight representative N-substituents (H, CH3, CHO, NH2, NO2, PH2, BH2 and BH−3) ab initio calculations at the 6-31G** level have been carried out. The average geometries for these groups of pyrazoles and those calculated theoretically are generally in good agreement considering the assumed simplifications (not taking into account the effect of the C-substituents, reduction of the N-substituent to its simpler expression). The effect of substituents on nitrogen parallels that on carbon in benzene rings with the exception of the amino group.