A link between fibromyalgia syndrome (FMS) and posttraumatic stress disorder (PTSD) has been suggested because both conditions share some similar symptoms. The temporal relationships between traumatic experiences and the onset of PTSD and FMS symptoms have not been studied until now. All consecutive FMS patients in 8 study centres of different specialties were assessed from February 1 to July 31, 2012. Data on duration of chronic widespread pain (CWP) were based on patients' self-reports. Potential traumatic experiences and year of most burdensome traumatic experience were assessed by the trauma list of the Munich Composite International Diagnostic Interview. PTSD was diagnosed according to the Diagnostic and Statistical Manual of Mental Disorders IV symptom criteria by the Posttraumatic Diagnostic Scale. Age- and sex-matched persons of a general population sample were selected for controls. Three hundred ninety-five of 529 patients screened for eligibility were analysed (93.9% women, mean age 52.3 years, mean duration since chronic widespread pain 12.8 years); 45.3% of FMS patients and 3.0% of population controls met the criteria for PTSD. Most burdensome traumatic experience and PTSD symptoms antedated the onset of CWP in 66.5% of patients. In 29.5% of patients, most burdensome traumatic experience and PTSD symptoms followed the onset of CWP. In 4.0% of patients' most burdensome traumatic experience, PTSD and FMS symptoms occurred in the same year. FMS and PTSD are linked in several ways: PTSD is a potential risk factor of FMS and vice versa. FMS and PTSD are comorbid conditions because they are associated with common antecedent traumatic experiences.