Low back pain (LBP) in occupational settings has been studied extensively. There are fewer studies on LBP in domestic settings, especially in an informal caregiving setting. To compare the prevalence of LBP in adult female primary caregivers of children with physical disabilities who need assistance with transfers (eg, moving from a bed to a wheelchair) with the prevalence of LBP in adult female primary caregivers of children with nondisabling medical illnesses and to evaluate the factors associated with LBP. A 15-minute, self-administered, cross-sectional survey. University-based clinics. Subjects Ninety consecutive adult female caregivers of children presenting to a pediatric physical medicine and rehabilitation clinic and 23 consecutive adult female caregivers of children presenting to a pediatric endocrine clinic were studied. General exclusionary criteria included the following: male sex, a history of back surgery or fracture, the caregiver was younger than 18 years old at the time of the completion of the questionnaire, or the caregiver was caring for any child younger than 2 years old. Caregivers visiting the pediatric endocrine clinic were excluded if they were caring for 1 or more children needing assistance with transfers. The dependent variable was the presence of LBP. The independent variables were mood, work status, amount of lifting at work, physical functioning of the child, demographic variables of the caregiver, and demographic variables of the child. The prevalence of having LBP (71.1%) in the physical medicine and rehabilitation group is higher than the prevalence (43.5%) in the endocrine clinic group (odds ratio, 3.2; 95% confidence interval, 1.25-8.21). The prevalence of having LBP (80.3%) when the child required physical assistance with transfers was significantly higher than the prevalence (40.5%) when the child did not require physical assistance with transfers (odds ratio, 2.56; 95% confidence interval, 2.56-14.0). Forward multiple logistic regression showed that the factors related to LBP in the caregiver were the transferability of the child, mood of the caregiver, and a history of LBP in the caregiver. The prevalence of LBP is higher in caregivers of children needing assistance with transfers. This increased prevalence is associated with the transferability of the child and mood of the caregiver. Results of this study suggest that physical and psychological factors both contribute to the presence of nonoccupational LBP.