Study design: Case-control study. Objectives: (i) To describe the prevalence of sexual dysfunction in chronic low back pain (CLBP) patients, (ii) to compare the range of sexual function outcomes between patients with CLBP and healthy controls and (iii) to investigate which factors are associated with sexual function within the cohort of individuals with CLBP. Setting: Low back pain (LBP) clinic of Qazvin University of Medical Sciences, Qazvin, Iran. Methods: A total of 702 patients with CLBP and 888 healthy controls participated in the study. The Female Sexual Function Index (FSFI), International Index of Erectile Function (IIEF) and Premature Ejaculation Diagnostic Tool (PEDT) were used to evaluate sexual function. In addition, quality of life, anxiety, functional status and pain intensity were assessed in patients. Univariate and multiple linear regression analyses were performed for the identification of factors associated with sexual function. Results: The prevalence of sexual problems in female patients with CLBP was 71.1% (n ¼ 177) while the corresponding figure for healthy women was 36.8% (n ¼ 161). Erectile dysfunction was present in 59.5% of male patients and in 24.5% of healthy males. Higher sexual function in both male and female patients with CLBP were being younger, lower duration of back pain, lower BMI, higher education level, being unemployed, physically active shorter sick leave, lower level of pain intensity, lower disability, higher family income, lower levels of depressive and anxiety symptoms, and higher psychical functioning and mental functioning. Conclusions: CLBP patients report considerably higher prevalences of sexual problems compared with healthy controls. Sex therapy and sexual management should be added to routine care and treatment of patients with CLBP.