OBJECTIVES: Gastrointestinal (GI) complications associated with immunosuppressants are frequently reported by renal transplant recipients. Mycophenolic acid has been associated with an increased incidence of GI complaints. GI complications may affect patient Quality of Life (QoL). The purpose of this study was to psychometrically validate two GI-specific patient-reported outcome (PRO) instruments in the renal transplant population. METHODS: The Gastrointestinal Symptom Rating Scale (GSRS) and Gastrointestinal Quality of Life Index (GIQLI) were selected for validation. Renal transplant recipients receiving a calcineurin inhibitor and mycophenolate mofetil were recruited in a cross-sectional study from 5 clinical centers across 4 countries. Patients completed the GSRS, GIQLI, Psychological General Well-Being Index (PGWB) and EQ-5D. Statistical analyses employed Cronbach’s alpha, correlations, t-tests and ANOVA. RESULTS: Of 96 patients recruited (mean age: 47.4 + 12.3 years; male: 56%), 41 (43%) suffered from no, 37 (39%) mild, 12 (13%) moderate, and 6 (6%) severe GI symptoms. Internal consistency reliability (Cronbach’s alpha) was > 0.7 for all GIQLI and all but 1 of the GSRS dimensions (abdominal pain). Correlations between GIQLI and PGWB and EQ-5D were higher (range: 0.24-0.76) than correlations between GSRS and PGWB and EQ-5D (range: 0.05–0.54). All GSRS subscales and the GIQLI total score and 4 subscales significantly differentiated between patients with and without GI complications (p<0.05), as did the PGWB total score and EQ-5D. The generic instruments were unable to discriminate between GI severity levels; conversely, the disease-specific instruments discriminated to some extent between GI severity levels. GSRS abdominal pain subscale discriminated between patients at all levels of severity (p<0.05). GIQLI total score and symptoms subscale discriminated among most severity levels (p<0.05). CONCLUSIONS: The GSRS and GIQLI demonstrated adequate reliability, and outperformed generic instruments on discriminant validity. Both instruments can be used to investigate effects on PRO's related to GI complications due to immunosuppressant therapies.