Phase 1 (P1) trials are vital to the development of cancer treatments; however, the patients involved in these trials are unlikely to receive any therapeutic benefit, and there are significant possibilities that they will experience serious side effects. Ethical requirements stipulate that patients must be adequately informed before they consent to participate in P1 trials. This review focuses on studies that have measured patient comprehension of information given during the informed consent process of P1 cancer trials. Patients consenting to participate in P1 trials currently have a limited understanding of trial purpose, an unrealistic expectation of the benefits and risks associated with trial participation and a questionable appreciation of their right to abstain or withdraw. Health care professionals recruiting to P1 trials need clear and practical guidelines and training packages designed to ensure that all details of P1 trials are communicated effectively to eligible patients.