The study objective was to investigate patient experienced error during diagnosis and treatment of cancer. included a nationwide patient survey on quality and safety in Danish cancer care. Responses regarding patient experienced error were separately analyzed, quan using systematic text analysis. Study participants included registered between May 1st and August 31st 2010 care received by general practitioners, specialist 10-25% of patients experienced error during diagnosis or treat consequences. Unexpected surgical errors/complications (27%), delay due to doctors' assessment errors (24%) and unavailable test results (21%) were the most frequent types of errors identified using closed questions. 819 qua responses supplemented this information and revealed errors related to cancer detection, planning & coordination, patient-provider communication, administrative processes and treatment & medication. Physical, psychological, social as well as organizational consequences of the errors were uncovered. related to informed consent, diagnostic reasoning as well as handling of test results, referrals and the medical chart should be further improved. In addition, safety aspects of the patient patients as an extra safety barrier merit further study.