Aim was to survey distinctive qualities of decision-related uncertainty in cancer. Assessment of differential perception of uncertainties is a prerequisite for the study of cognitive coping as mediated by risk communication. A theory building process was initiated. Using in-depth interviews with cancer patients subjective representations of uncertainty associated with medical decisions were explored. Grounded theory techniques were applied to extract categories out of the interview material. The qualitative process led to an eight-dimensional model. Five raters achieved a Fleiss agreement coefficient of 0.61 attributing raw material from interviews to the categories. Patients expressed uncertainties concerning (1) disease-related issues (prognosis/diagnosis, treatment), (2) risk communication issues (deciphering information, role in the medical dyad, physician's trustability) and (3) aspects of coping with life considering the disease (mastering requirements, social integration, causal attribution). We found support for a multidimensional model of uncertainty. This approach can be helpful in the investigation of further issues concerning communication and coping with uncertainty related to medical decisions in cancer and other diseases. It sharpens shared decision making theoretically and thereby provides the basis for a measurement concept.