Case formulation is at the heart of personalised care in psychotherapy. Scientific research into case formulations can provide new insights in the heterogeneity of psychopathology which are relevant for advances in personalised psychopathology research and practice. This mixed-methods study examined the content of 483 fully personalised network-based case formulations in psychotherapy in terms of uniqueness (i.e., frequencies of concepts) and commonality (i.e., the presence of common themes over the different case formulations). In a real-world clinical care setting, patients co-created network-based case formulations with their therapist as part of their routine diagnostic process. These case formulations feature concepts that are relevant to individual patients and their current situation. We assessed how often concepts were used by different patients to quantify uniqueness. We applied a bottom-up thematic analysis to identify patient-relevant themes from the concepts. The case formulations of 483 patients diagnosed with mood and/or anxiety disorders contained a total of 4908 interpretable concepts of which 4272 (87%) were completely unique. Through thematic analysis, we identified seven overarching themes in the concepts: autonomy, connectedness, emotions, self-care, identity, self-efficacy, and bodily sensations. Case formulations were highly unique, thereby illustrating the importance of personalised diagnostics. The unique concepts could be grouped under seven overarching themes which seem to encompass basic human needs. Current advancements in personalised diagnostics and assessment should have a broader scope than symptoms alone, and could use the themes identified here as part of a topic list in the generation of (network-based) case formulations.