Many trials on Internet-delivered psychological treatments have had problems with nonadherence, but not much is known about the subjective reasons for non-adhering. The aim of this study was to explore participants' experiences of non-adherence to Internet-delivered psychological treatment. Grounded theory was used to analyze data from seven in-depth interviews with persons who had non-adhered to a study on Internet-delivered cognitive behavioral therapy for generalized anxiety disorder. The process of non-adherence is described as an interaction between patient factors and treatment factors. A working model theory was generated to illustrate the experience of nonadherence. The model describes a process where treatment features such as workload, text-content complexity and treatment process don't match personal prerequisites regarding daily routines, perceived language skills and treatment expectations respectively, resulting in the decision to nonadhere. Negative effects were also stated as a reason for non-adherence. Several common strategies used for increasing adherence to Internet-delivered therapy in general are by these non-completers regarded as factors directly related to their reason for non-adherence.