OBJECTIVE. The aim of this study was to determine the reliability of the Box and Block (B&B) Test of Manual Dexterity for upper-extremity function in patients with fibromyalgia and to compare their results with those of healthy control participants. METHOD. We assessed reliability of the B&B Test within and between testers using the intraclass correlation coefficient (ICC). We compared fibromyalgia patient ( n = 30) and control group ( n = 30) scores using analysis of variance and population-based normative data. RESULTS. The B&B Test was reliable with ICCs of .90 to .85. Fibromyalgia patients’ B&B Test scores were significantly lower (more impaired) than those of the control group and standardized norms. CONCLUSIONS. The B&B Test is a reliable measure of upper-extremity function in fibromyalgia patients and is able to reveal a reduction in upper-extremity function in these patients compared with both healthy control participants and normative scores.