Post-transplant diabetes mellitus (PTDM) is common after most types of solid organ transplantation, though the actual incidence is as yet unknown because of the use of different diagnostic criteria. PTDM is the result of individual risk factors as well as risk factors associated with the transplant itself, particularly immunosuppressants. Previously called New Onset Diabetes, in many cases inadequate screening for diabetes before transplant cannot assure that the diabetes is new after transplant. The most recent international consensus guidelines suggest diagnosis should be delayed until the patient is taking maintenance doses of immunosuppressants even if they require treatment in the immediate hospitalization. Criteria for diagnosis follow those of the American Diabetes Association and the World Health Organization, although hemoglobin A1C should not be used as the only screening test at least until one year after transplant because of its insensitivity for significant glucose intolerance in the transplant patient and setting. Management of PTDM is best done in a team setting, with an emphasis on glycemic control, dyslipidemia, and hypertension, and taking into consideration immunosuppressant regimens and potential drug side effects and interactions. While PTDM has been associated with changes in outcomes, these have and may continue to improve with improved diabetes care in and out of the hospital, and other changes in post-transplant care.