Background: Fibromyalgia syndrome (FMS) is a chronic musculoskeletal condition, which can reduce the quality of life (QoL). Objectives: This study aimed to evaluate the impact of FMS on health-related quality of life (HRQoL) and the possible related factors such as sociodemographic and psychological variables. Methods: In this cross-sectional study, 150 women patients with FMS were included who visited a psychosomatic clinic at a referral center in northern Iran. The samples were selected in a consecutive procedure from April 2019 to March 2019. Sociodemographic variables, HRQoL score [36-Item Short Form (SF-36) Health Survey], and the Pittsburgh Sleep Quality Index (PSQI) were recorded. Data were analyzed using the SPSS Statistics software (ver. 24). The quantitative data were reported as mean ± SD, and the qualitative variables were presented as frequency and percentage. Also, analysis was performed using analytical tests such as chi-square test (χ2). P < 0.05 was considered to be significant. Results: The mean (SD) age was 42.35 (11.73) years. The mean physical and mental health scores were 33.45 (16.22) and 48.99 (18.19), respectively. Moreover, 88% of patients had moderate-to-severe sleep disorder, and those who did not, had a better physical and mental health status [42.7 (14.1) vs. 32.2 (16.1), P-value = 0.009 and 62.2 (16.3) vs. 47.2 (17.7), P-value = 0.001, respectively]. History of depression according to self-reporting was associated with worse mental health subscale scores [44.4 (16.8 Vs. 52.4 (18.5), P-value = 0.007], and lower scores in social functioning and emotional well-being (P-value = 0.012, P-value = 0.001, respectively). Being postmenopausal was associated with a lower physical health quality (P-value = 0.049). Body Mass Index (BMI) reversely correlated with HRQoL subscales (r = -0.163, P-value = 0.046), but the subscales were not affected by the level of income (P-value = 0.644, P-value = 0.170, respectively). Conclusions: Patients with fibromyalgia report a considerable significant impact on their quality of life and impaired sleep quality. Assessment of sleep quality and QoL are needed in patients with fibromyalgia.