Multiple sclerosis (MS) burdens not only patients but also their informal or family caregivers. This study was conducted to identify characteristics of caregivers, caregiving, and MS patients receiving informal care that are associated with caregiving burden. Data were collected through a national survey of informal MS caregivers and analyzed using an ordered logistic regression model to identify factors associated with burden. Burden was found to be significantly greater among male caregivers than among female caregivers. Moreover, greater burden was associated with more frequent patient bladder dysfunction, more hours per week spent providing assistance, and greater restriction on the caregiver's ability to perform daily activities because of caregiving responsibilities. A strong association was found between the mental health status of the caregiver and burden. Health professionals should be sensitive to the impact of caregiving on the mental health of MS caregivers. The results of this study suggest that treating patient bladder dysfunction and facilitating respite care may reduce burden and improve the mental health of informal caregivers of people with MS. Future research should identify programs and services designed specifically to reduce burden experienced by male caregivers. Int J MS Care. 2011;13:76-83.