In parallel with a randomized study of the 'starting again' rehabilitation program for cancer patients, a group of 73 non-participants were monitored (another 20 patients declined monitoring). In comparison with participants (intervention + control), gender, diagnosis, and 10 out of 18 dependent measures differed significantly at baseline. The non-participants group included more men, mostly with cancer of the prostate and irrespective of gender, they showed lower problem levels than participants throughout. Thus, the wish to participate seems to be an indicator of the need for assistance in the rehabilitation process. Social validation of effects was performed by comparing the non-participants with the intervention group. The rationale for this comparison is that non-participants presumably felt so well that they were in no need of rehabilitation. Effects on three variables were socially validated: patients' appraisal of having received sufficient information, physical strength and fighting spirit. No negative effects on outcome variables resulting from being randomized to the control condition (resentful demoralization) were detected when non-participants were compared with controls over one year. Further analysis showed that although a few patients in the control group may have experienced resentful demoralization, this did not significantly affect the outcome variables.