The ability to correctly estimate the sex of skeletal remains is vital in forensic sciences. This article investigates the sexual dimorphism of the human sacro-iliac joint, using geometric morphometric techniques that assess morphological characters better than the traditional approaches for recording outline shapes, which are subject to quantification and inter-observer problems. Eight two-dimensional landmarks were recorded from digital images of 29 female and 35 male auricular surfaces of the ilium and sacrum. The specimens were analyzed using geometric morphometric methods (Generalized Procrustes analysis, relative warp analysis, Goodall's F) and multivariate statistics (ANOVA, MANCOVA, principal component analysis, discriminant function analysis [DFA]). Both the size and shape of the analyzed structures were found to be sexually dimorphic. The DFA illustrated that when the form of both the iliac and sacral articular surface is taken as a predictor variable, 94.5% of the individuals are assigned to the correct sex. The successful sex determination obtained by the DFA makes the further study of the sacro-iliac joint's sexual dimorphism promising.