Background: Relational satisfaction of spousal/partner informal caregivers of people with multiple sclerosis (MS) is important for continued care and support. Previous studies have examined relational satisfaction in terms of well-being and quality of life of informal caregivers. Based on the Rusbult investment model, we directly studied the relational satisfaction of spousal/partner informal caregivers of individuals with MS. In doing so, we investigated possible effects that commitment to relationship, caregiving burden, and prorelational behavioral tendencies might have on relational satisfaction. Methods: Nine hundred nine adult spousal/partner informal caregivers of people with MS completed measures of relational satisfaction (Kansas Marital Satisfaction Scale), commitment to relationship (15-item commitment measure), caregiving burden (Zarit Burden Interview), and prorelational behavioral tendencies (adapted Prosocial Tendencies Measure). Participants also provided demographic information (age, sex, duration and type of relationship [spouse, partner]). Results: Structural equation modeling highlighted commitment to the relationship as the strongest predictor of relational satisfaction. Caregiving burden was found to affect relational satisfaction directly and through commitment to relationship. Prorelational behavioral tendencies were found to affect less relational satisfaction. Conclusions: Commitment to relationship, namely, intent to persist, had the highest positive effect on satisfaction. Caregiving burden was found to have a two-way negative relationship to commitment to relationship. These findings suggest that specialists should enhance the intent-to-persist aspect of commitment because it seems to have an alleviating effect regarding caregiving burden (which itself negatively affects relational satisfaction).