Objective: To enhance insight into the process of occupational therapy (OT) and the changes after OT, in an older patient with mild dementia and his primary caregiver. Design and setting: Case study: content analysis of an OT patient record. Intervention: System-based OT at home using a guideline focusing on both patient's performance in daily activities and caregiver's cognition on patient behaviour and caregiver role and focusing on adaptation of the physical environment. Measures: Triangulation of results of qualitative content analysis and quantitative description using the following measures: Brief Cognitive Rating Scale (BCRS), Assessment of Motor and Process Skills (AMPS), Interview of Deterioration in Daily Activities in Dementia (IDDD), Canadian Occupational Performance Measurement (COPM), Dementia Quality of Life Instrument (DQOL), Sense of Competence Scale (SCQ) and the Mastery Scale. Results: The global categories derived from content analysis were: daily performance and communication. The specific categories were the patient with dementia, his or her caregiver and the occupational therapist. Important themes derived from content analysis were: patient's capacity for pleasure, autonomy and appreciation in performing daily activities and caregiver's competence. Patient's changes reported after OT: more initiative, autonomy and pleasure in performing daily activities, increase of quality of life; caregiver's changes reported after OT: improved communication and supervision skills, changed cognition on patient behaviour and caregiver role, improved sense of competence. The quantitative results showed an improved daily performance (e.g. initiative, motor and process skills, need for assistance) and quality of life of the patient and improved sense of competence, quality of life and mastery of the situation of the caregiver after OT intervention. Thus the results of the qualitative content analysis were supported by the quantitative results. Additionally, based on the results of the content analysis an exploratory and system-based model has been developed connecting OT diagnosis and OT treatment at home for patients with dementia and their primary caregivers. Conclusion: This case study provides information on how occupational therapy can improve the daily performance, communication, sense of competence and quality of life of an older patient with dementia and his or her primary caregiver. A combination of education, setting feasible goals, using adaptations in physical environment, training compensatory skills, training supervision skills, and changing dysfunctional cognitions on patient behaviour and caregiver role seemed to be successful. A randomized controlled trial must provide information on the effects of OT at home for older patients with dementia and their primary caregivers.