The Guideline Colorectal Cancer has been existed since 1999. In 2004, a revision was published in form of the S3-guideline (number of the AWMF registry: 021/007). In this study we aimed to evaluate whether diagnostics and therapy of colorectal cancer of younger patients (<65 years) in Schleswig-Holstein (SH) were in accordance with the guideline or not. Therefore patients from a molecular genetic research project ("popgen") were asked to complete a questionnaire regarding their medical care. Data from the self-administered questionnaire and from the routine data set of the epidemiological cancer registry SH were available for 245 patients (mean age: 56.9 years; 48.6% were females). Nearly 54% of the patients had a tumour located in the colon and 42.9% in the rectum. Most patients (65.7%) experienced locally progressing tumours (T3/T4). Positive lymph nodes were diagnosed in 41% of the patients, distant metastases in less than 1%. About 88% had a coloscopy, 62.4% an X-ray of the lung, and 78.7% a sonography of the abdomen in the course of the preoperative diagnostics. Of all patients, 97.1% have been operated. An adjuvant radiation was received by 31.7% and adjuvant chemotherapy was given to 36.3% of the patients. In order to assess medical care, reference values were defined for specific phrasings from the S3-guideline (e.g., "always indicated": > 95%). According to the data from the patients' questionnaires and according to the S3-guideline, quality indicators of the preoperative diagnostics in SH were beneath the assumed reference values. But the data on therapy procedures indicated a good or at least satisfactory medical care.