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Objective This study investigated whether chronic constipation and diarrhoea are temporally linked to colorectal cancer (CRC) diagnosis, aiming to clarify if these symptoms function as modifiable risk factors or early indicators of malignancy.Methods We conducted a retrospective case–control study using real-world data from the German Disease Analyser database. After 1:5 propensity score matching for age, sex, index year and comorbidities, 10 941 patients with CRC and 54 705 matched controls without cancer were included in the study. Documentation of constipation and diarrhoea was evaluated in six time intervals up to 5 years before CRC diagnosis. Multivariable conditional logistic regression was used to calculate ORs and 95% CIs for CRC risk.Results Constipation was significantly more frequent in patients with CRC within 6 months prior to CRC diagnosis (OR 3.23; 95% CI 2.85 to 3.66). A similar pattern was observed for diarrhoea within 6 months prior to diagnosis. However, the association was stronger the more frequently diarrhoea was documented (at least one diagnosis: OR 3.37; 95% CI 3.03 to 3.75; at least two diagnoses: OR 4.18; 95% CI 3.31 to 5.28; at least three diagnoses: OR 6.82; 95% CI 4.43 to 10.49). No associations were identified beyond 1 year before diagnosis.Conclusion Constipation and diarrhoea were associated with the subsequent diagnosis of CRC only in the immediate months before diagnosis, suggesting reverse causality rather than a causal relationship. These symptoms may serve as red flags rather than risk factors, emphasising the need for timely diagnostic evaluation, especially in the presence of persistent changes in bowel habits.