Identifying a hereditary colorectal cancer (CRC) syndrome or familial CRC (FCC) in a CRC patient may enable the patient and relatives to enroll in surveillance protocols. As these individuals are insufficiently recognized, we evaluated an online family history tool, consisting of a patient-administered family history questionnaire and an automated genetic referral recommendation, to facilitate the identification of patients with hereditary CRC or FCC. Between 2015 and 2016, all newly diagnosed CRC patients in five Dutch outpatient clinics, were included in a trial with a stepped-wedge design, when first visiting the clinic. Each hospital continued standard procedures for identifying patients at risk (control strategy) and then, after a predetermined period, switched to offering the family history tool to included patients (intervention strategy). After considering the tool-based recommendation, the health care provider could decide on and arrange the referral. Primary outcome was the relative number of CRC patients who received screening or surveillance recommendations for themselves or relatives because of hereditary CRC or FCC, provided by genetic counseling. The intervention effect was evaluated using a logit-linear model. With the tool, 46/489 (9.4%) patients received a screening or surveillance recommendation, compared to 35/292 (12.0%) in the control group. In the intention-to-treat-analysis, accounting for time trends and hospital effects, this difference was not statistically significant (p = 0.58). A family history tool does not necessarily assist in increasing the number of CRC patients and relatives enrolled in screening or surveillance recommendations for hereditary CRC or FCC. Other interventions should be considered.