Background In the German National Cohort (NAKO Gesundheitsstudie), the largest prospective cohort study in Germany, data on self-reported cancer diagnoses are now available for the first half of participants. Objectives Description of the methods to assess self-reported cancer diagnoses and type of cancer in the NAKO and presentation of first results. Materials and methods In a computer-assisted, standardized personal interview, 101,787 participants (54,526 women, 47,261 men) were asked whether they had ever been diagnosed with cancer (malignant tumors including in situ) by a physician and how many cancer diagnoses they had. The type of cancer was classified with a list. Absolute and relative frequencies of self-reported cancer diagnoses and types of cancer were calculated and compared with cancer registry data. Results A physician-diagnosed cancer was reported by 9.4% of women and 7.0% of men. Of the participants who reported a cancer diagnosis, 88.3% reported to have had only one cancer diagnosis. In women, the most frequent malignancies were breast cancer, cervical cancer, and melanoma. In men, the most frequent malignancies were prostate cancer, melanoma, and colorectal cancer. Comparing the frequencies of cancer diagnoses reported by 45- to 74-year-old NAKO participants within the last five years to cancer registry-based 5-year prevalences, most types of cancer were less frequent in the NAKO, with the exception of melanoma in men and women, cervical cancer and liver cancer in women, and bladder cancer and breast cancer in men. Conclusions The NAKO is a rich data basis for future investigations of incident cancer.