OBJECTIVES: To develop and validate a clinically useful instrument for assessing the impact of gastrointestinal symptoms (GI) on the health-related quality of life (HRQoL) of solid organ transplant (SOT) patients (kidney, liver, heart or lung). METHODS: Two phases: the Mypaciente-1 study was an epidemiological, cross-sectional, multicentre study in which the SIGIT-QoL® questionnaire (17 items) was developed and its reliability, feasibility and validity (content and construct) were proven. At second, an observational, prospective, multicentre study, the Mypaciente-2, was implemented to assess the test-retest reliability and the sensitivity to change of the SIGIT-QoL®. SOT patients aged≥18, who had received the graft 3-24 months before and suffering from GI, were evaluate at baseline, 1-2 weeks and 3 months after baseline. Data recorded: age, sex, SOT type, acute allograft rejection (AAR), GI etiology, Clinical and Patient global Impression scale (CGI-SI&GI and PGI-SI&GI) and the SIGIT-QoL® (range: 0-maximum impact to 68-minimum disruption). Intraclass correlation (ICC), differences between baseline and last visit (Wilcoxon test), effect size (Cohen’s d), the minimal important difference –MID- (using CGI & PGI as anchors in General Linear Models) and the cut-off score (ROC  analysis) were calculated. RESULTS: In the Mypaciente-2 study 277 SOT patients (61.4% males) were included. Mean age (SD) was 52.69(11.65) years, time since transplantation was 12.31(6.74) months and 22.4% suffered AAR. At baseline, SIGIT-QoL® scores: 51.21(11.25) showed an impact on patients’ HRQoL that diminished 3 months later: 57.40(8.38;p<0.001). SIGIT-QoL® test-retest reliability was adequate (ICC=0.740-0.895). A high-moderate effect size (d=-0.590) was found. Moreover, MID of 4.2 points in total scores were found (F4,223=16.917,p<0.001 and F4,224=25.138,p<0.001). Finally, a cut-off point (55.00 points) was estimated (AUC=0.846,p<0.001; sensitivity=0.793; specificity=0.713; negative likelihood ratio=0.290; positive likelihood ratio=2.762). CONCLUSIONS: The SIGIT-QoL® is a feasible (average completion time lower than 6.5 minutes), reliable and valid instrument for assessing the impact of GI symptoms on SOT patients.