For a study, researchers sought to understand that psychological abilities are more important than physical abilities in today’s world. Patients suffering from neurological disorders have not only physical but also psychological limitations. Because comorbidity of neurological and mental disorders occurs in many cases, the question is to what extent this can increase psychological incapacity. Neurological patients with and without mental comorbidity were recruited using a cross-sectional study design in a neurological phase D rehabilitation department. A total of 114 patients with neurological and mental disorders (NM) were compared to 214 unselected patients with only neurological disorders (N). The standardized “International Neuropsychiatric Interview” was used to diagnose mental comorbidity. The “Activities and Participation in Psychological Disorders according to the International Classification of Functioning, Disability, and Health” scale assessed capacity limitations (Mini-ICF-APP). The Mini-ICF-APP ratings were validated using patient qualitative reports. Clinical diagnoses were derived from routine patient assessments. Severe capacity limitations, requiring assistance from others, were observed in particular for endurance (NM: 73.7% vs. N: 59.8% of patients), flexibility (NM: 43.0% vs. N: 22.4%), professional competency (NM: 36.0% vs. N: 16.8%), and task structuring (NM: 32.5% vs. N: 15.0%). Impairment in dyadic relationships was the least common (NM: 23.7% vs. N: 7.9%). The rank order and qualitative descriptions of impairments were similar in both groups. Patients with neurological disorders, in general, had significant capacity limitations. It was exacerbated further by mental comorbidity. Specific treatment was required.