Costimulatory molecules have complementary effects on T-cell activation and their balance may control the development of oral cancer. The aim of this study was to determine the relevance of cytotoxic T-lymphocyte antigen 4 (CTLA-4), CD28 and inducible costimulator (ICOS) polymorphisms in oral squamous cell carcinoma (OSCC). Genotyping for CTLA-4 (-1661 A/G and +49 A/G), CD28 (0 C/G and +3160 G/T) and ICOS (+637 A/C and +1599 C/T) was performed in the 83 patients with OSCC, compared to the 40 unrelated healthy volunteers as controls. The genotype CTLA-4 -1661 was significantly different between the patient group and the control group. The allele CTLA-4 -1661 G was significantly found more frequent in patients with OSCC (p=0.001). In bivariate analysis, noticeable differences between OSCC and controls were seen. The combinations CTLA-4 -1661 G/G and CTLA-4 +49 A/G, ICOS +1559 C/T and ICOS +1559 C/C each with CTLA-4 -1661 G/G, ICOS +637 C/C and ICOS +637 A/C each with CTLA-4 -1661, CTLA-4 -1661 A/G and ICOS +637 C/C, CD28 +3160 G/T and CTLA-4 -1661 A/A and CD28 +3160 G/T and CTLA-4 -1661 A/G were seen in the patient group only. Especially the polymorphisms of the CTLA-4 -1661-genotype - alone and in combination with other T cell regulator polymorphisms - seem to be possible predisposing factors for OSCC. Therefore, they might be future targets for a primary prophylaxis or an individualised therapy.