Abstract Background Alterations in glucose metabolism are one of the most important complications of renal transplant recipients. The aim of this study was to analyze their prevalence and determinants and assess their influence on the main long-term clinical outcomes in a cohort of kidney transplant recipients. Methods we retrospectively analyzed the data of 832 kidney transplant recipients between 2004 and 2020 in our center. Patients were studied at 1 (T1), 6 (T6), and 12 (T12) months after transplantation and followed clinically for a follow-up time of 103 ± 60 months. At T6, an oral glucose tolerance test (OGTT) was performed in 484 patients. Results The mean age of the cohort studied was 49 ± 13 years, with a mean dialysis vintage of 54 ± 52 months. Hemodialysis was the therapy before KTx in 70.6% of patients, whereas 20.9% had been treated with peritoneal dialysis. The 8.5% of patients received a pre-emptive KTx. Fifty-seven percent of the patients were male and 83.5% had a KTx from a deceased donor. Both at T1 and T12, immunosuppressive therapy was mainly composed of steroids (average cumulative dose at T12: 2914 ± 962 mg), calcineurin inhibitors and mycophenolate. In our cohort at T12, diabetic patients were 237 (28.6%), of which 51 (6.2%) were already affected by diabetes before KTx. Of note, we diagnosed diabetes by OGTT in 23 KTxps, while in 90 KTxps, OGTT showed prediabetic alterations. Patients with glucose metabolism abnormalities were significantly older, had an altered lipid profile associated with higher BMI values and a significantly higher inflammatory index. Interestingly, our data showed that graft loss was not affected by any type of alteration of glucose metabolism. On the contrary, we found that mortality was significantly higher in patients with pre-transplant diabetes and in those with alterations in glucose metabolism detected with OGTT (both including diabetes and considering only IGT and IFG). Conclusions Our data showed that age at transplantation, lipid profile, and the inflammatory state were the variables that most influenced the development of PTDM. Interestingly, mortality was significantly associated with pre-transplant diabetes and alteration in glucose metabolism. This allowed us to highlight the impact of prediabetes status and the importance of OGTT as a screening test in post-transplant and potentially pre-transplant. Future randomized controlled trials will be able to resume the topic, including the analysis of the effects of new antidiabetic drugs.