Serum from 386 myeloma patients were analyzed for serum hyaluronan (HYA) at diagnosis. Median age was 68 years (range, 32 to 87 years). The distribution of Ig classes was typical (58% IgG, 21% IgA, 1% IgD, and 20% light chain disease). The patients comprised 58% in stage III, 33% in stage II, and 9% in stage I. The majority (82%) had HYA values within an intermediate range (10 to 120 micrograms/L), 13% had high values (>120 micrograms/L), and 5% had abnormally low values (0 to 9 micrograms/L). For the first time, a patient group with abnormally low HYA serum values is reported. An inverse correlation between survival and HYA serum level was found (P =.015). When tested separately, patients with abnormally low or high HYA values had significantly shorter median survival (21.1 and 19.7 months, respectively) than those with an intermediate HYA concentration (32. 6 months; P =.005). Patients with abnormally low or high HYA levels had more advanced disease as judged by staging and biochemical markers. Interestingly, there was an inverse correlation between the HYA value and the M-component concentration in serum. Fifty percent of patients with abnormally low HYA values had IgA myelomas. In conclusion, the serum concentration of HYA may be of prognostic value in selected cases of multiple myeloma. Further studies will be performed to elucidate possible explanations for our findings, especially those related to the HYA cell surface binding proteins.