BACKGROUND AND OBJECTIVES: Musculoskeletal pain affects 3% to 5% of the world population, decreasing patients' functional capacity. This study aimed at comparing functional capacity among females with fibromyalgia or low back pain. METHOD: Comparative study with convenience sample of 69 females with diagnosis of low back pain (35) or fibromyalgia (34) registered in the Orthopedics Outpatient Setting of a Public Teaching Hospital in Fortaleza/CE. Musculoskeletal Pain Evaluation Questionnaire was used, and the association among type of pain, sociodemographic characteristics and activities practiced by patients was analyzed with Chi-square (χ 2) and Fisher-Freeman-Halton tests. RESULTS: From 69 participants, mean age was 45 ± 10.8 years, most were married (63.8%), most had (42.0%) low education level and were housewives (37.7%). The type of pain had no statistically significant association with marital status (p = 0.289), occupation (p = 0.349) and education level (p = 0.907). Major pain site for both groups was lumbar spine (56%) and was insidious (69%) and continuous (54.5%). Most did not practice physical exercises (p < 0.001), and complained of lack of energy, especially those with fibromyalgia (82.4%) (p = 0.019). From mentioned physical activities, walking was predominant in both groups (52.6%), followed by stretching, gymnastics and hydrogymnastics (47.4%) (p = 1.000). There has been impairment of occupational (21.7%), domestic (21.7%) and leisure (13.0%) activities. CONCLUSION: Females with fibromyalgia had poorer functional capacity as compared to females with low back pain, deserving attention of health professionals for thorough pain evaluation, and assessment of functional changes of these patients.