We examined the feasibility and the proportional trade-off assumption of the Time Trade-Off method. Utilities were assessed of the actual health states of 54 testicular and 72 colorectal cancer patients, treated with the curative intent and 29 incurable colorectal cancer patients. Three periods of time were used to assess proportionality: the subject's life expectancy and two shorter periods. Results showed the method to be feasible in curatively treated patients, though the use of life expectancy posed difficulties in some very old subjects. This same difficulty was encountered in patients with symptomatic incurable disease. A two step procedure is proposed as a solution. The proportional trade-off assumption was violated. Utilities for the longer period were smaller than those for the shorter periods. Life expectancy and trade-off did not correlate, though. Remarkable was that many patients were unwilling to trade at all. The implications of the findings are discussed.