Background: Recent results of a randomized clinical trial showed that a guided self-help intervention (based on problem-solving therapy) targeting psychological distress among head and neck cancer and lung cancer patients is effective. This study qualitatively explored motivation to start, experiences with and perceived outcomes of this intervention. Methods: Data were collected from semi-structured interviews of 16 patients. All interviews were audio-recorded and transcribed verbatim. Data were analyzed individually by two coders and coded into key issues and themes. Results: Patients participated in the intervention for intrinsic (e.g. to help oneself) and for extrinsic reasons (e.g. being asked by a care professional or to help improve health care). Participants indicated positive and negative experiences with the intervention. Several participants appreciated participating as being a pleasant way to work on oneself, while others described participating as too confrontational. Some expressed their disappointment as they felt the intervention had brought them nothing or indicated that they felt worse temporarily, but most participants perceived positive outcomes of the intervention (e.g. feeling less distressed and having learned what matters in life). Conclusions: Cancer patients have various reasons to start a guided self-help intervention. Participants appreciated the guided self-help as intervention to address psychological distress, but there were also concerns. Most participants reported the intervention to be beneficial. The results suggest the need to identify patients who might benefit most from guided self-help targeting psychological distress and that interventions should be further tailored to individual cancer patients’ requirements.