BACKGROUND: Persons with conditions causing mobility impairment such as multiple sclerosis (MS), Parkinson's disease (PD) and stroke (CVA) do not have accessible resources or programs that promote and sustain exercise engagement. OBJECTIVE: This study explored perceptions of fitness facility exercisers with MS, PD and CVA, and adapted fitness center trainers, regarding a decision support system (DSS), and its design and components, for promoting, guiding, and sustaining exercise engagement. METHODS: Fitness facility exercisers (n= 15) and adapted fitness center trainers (n= 5) partook in semi-structured qualitative interviews. The interviews were audio-recorded and transcribed verbatim. We applied thematic analysis and identified themes and sub-themes regarding perceptions, design features, and components of a DSS for promoting, guiding, and sustaining exercise engagement. RESULTS: All fitness facility exercisers and adapted fitness center trainers believed that a DSS would be a beneficial tool for exercise prescription and progression. There were concerns about individualization and safety, and participants felt that a DSS should include evidenced-based, disease-specific, and individualized exercise prescriptions as well as prescreening for contraindications and fall risk. The participants further reported that behavioral change strategies were desirable for promoting and sustaining exercise participation. CONCLUSION: The study results identified perceptions and desired features of a DSS for promoting, guiding, and sustaining exercise engagement among individuals with conditions causing mobility impairment. This information will guide development of a prototype for subsequent usability and feasibility testing.