BACKGROUND Data on the effectiveness of once-daily tacrolimus (Tac-QD) in simultaneous pancreas-kidney (SPK) transplant patients are limited, which is of particular concern because diabetic gastroparesis may affect absorption. The aim of this study was to evaluate the clinical impact of converting SPK patients from twice-daily (Tac-BD) to Tac-QD. METHODS From November 2008 to August 2011, 27 SPK recipients (out of 130) were converted from Tac-BD to Tac-QD. Demographics, prescribed doses, trough levels, and creatinine, glucose, and HbA1c values were collected prospectively at the time of conversion and at 1, 2, 3, 6, and 12 months after conversion. RESULTS The mean time from transplantation to conversion was 35.81 ± 27.31 months, with 20 patients (74.07%) converted to Tac-QD >12 months after transplantation. There were no significant differences in the tacrolimus dose and trough levels before and after conversion and at all points during the follow-up. Creatinine, glucos,e and HbA1c levels remained stable throughout. Eight patients (29.63%) with gastroparesis had clinical outcomes, drug doses, and trough levels similar to all other patients. CONCLUSIONS Stable SPK recipients can safely be converted from Tac-BD to Tac-QD, with no clinical impact on the transplant function. Gastroparesis does not appear to influence tacrolimus dose requirements or trough levels.