- Fibromyalgia syndrome (FMS) is common, consisting of diffuse aching, pain, or stiffness in the muscles or joints. A recent study found an association between FMS and the short version of the serotonin transporter promoter region polymorphism (HTTLPR). That study prompted us to genotype a group of 99 female FMS patients from two Israeli ethnic groups. We also assessed each patient with the tridimensional personality questionnaire (TPQ). Similar to the German study, we found that the percentage of patients characterized by the short/short genotype is twice that observed in the control population (35% versus 17%). The difference in 5-HTTLPR genotype frequencies between the FMS and control group was highly significant (chi-square = 25.31, P = 0 .00019 df=2). This difference was also significant when each ethnic group was separately examined with its appropriate ethnically matched control group (Bedouin: chi-square = 15.10, P = 0.001; Jewish: chi-square = 7.47, P = 0.024). A highly significant effect of diagnosis was observed on three of the TPQ personality traits. Additionally, a significant association (F = 6.21, P = 0.01) was observed in the patient group between TPQ Harm Avoidance and the HTTLPR polymorphism and patients with the short genotype had higher Harm Avoidance scores.