Common polymorphisms in the transcription factor 7-like 2 gene (TCF7L2) have been associated with type 2 diabetes in different populations and recently with LADA, but not with type 1 diabetes. The aim of our study was to investigate association between the rs7903146 polymorphism in the TCF7L2 gene and LADA in Polish patients. Link between the “high risk for type 2 diabetes genotype” with clinical features was analyzed. 68 newly diagnosed patients with LADA and 195 healthy controls were genotyped for the rs7903146 polymorphism in the TCF7L2 gene using the PCR-based RFLP method. Fasting C peptide level was measured by ELISA. We observed increased frequencies of the TT genotype of the rs7903146 polymorphism in the TCF7L2 gene in LADA patients compared to controls (15 vs. 6%, P = 0.03). Fasting C peptide serum concentration was significantly lower in group of patients with LADA carrying the TT genotype (P < 0.01). In conclusion, the data from this study confirmed previous results showing genetic similarities between patients with LADA and type 2 diabetes. Non-autoimmune mechanism may be related to beta cell dysfunction in patients with LADA.