BACKGROUND: Irritable bowel syndrome (IBS) represents the most common functional disorder of the gastrointestinal tract. Many patients with IBS display complex gastrointestinal (GI) symptoms leading to overlapping diagnosis of IBS and other GI diseases in many patients. METHODS: Using the Disease Analyzer database (IQVIA) featuring patients treated within 2010 and 2019 within 1240 general practices in Germany, we analyzed the prevalence of common GI diseases within 12 months prior to and after the first diagnosis of IBS. RESULTS: 65,569 patients with an initial diagnosis of IBS were included into the analysis. Out of these, 29,553 patients had an observation time of at least 12 months prior to the first IBS diagnosis and at least 12 months after the first IBS diagnosis. Mean age was 48.8 (SD: 18.4) years, 65.0% were female. Notably, 16,164 (55%) of these patients had at least one preexisting diagnosis of another GI diseases within 12 months prior to the first IBS diagnosis. Most common overlapping diagnoses were intestinal infectious diseases (26%), gastritis/ duodenitis (21%), diseases of the esophagus (15%), non-infectious enteritis or colitis (7.4%), functional dyspepsia (6%) and ulcers (1.0%). Additionally, 12,048 (41%) received one of these diagnosis within 12 months after the first IBS diagnosis. CONCLUSION: Our data provide evidence for a high overlap between IBS and other GI diagnoses. Moreover, we show that IBS is frequently diagnosed in patients with preexisting GI diseases, potentially putting into question the validity of IBS diagnosis at least in some cases.