A patient with biopsy-proven papular mucinosis, plus the characteristic IgG lambda light chain paraproteinemia, also developed a severe proximal myopathy, seronegative inflammatory polyarthritis, and marked eosinophilia. Muscle enzymes were elevated, EMG was compatible with polymositis, and muscle biopsy revealed an atypical necrotizing vacuolar myopathy. Synovial biopsy revealed an inflammatory synovitis with Class II synovial fluid. No mucin deposition was detectable in muscle or synovium. During 7 years of observation, corticosteroids and various immunosuppressive agents were successively administered with little benefit. Recently, weekly intravenous methotrexate and low-dose oral corticosteroids have resulted in clinical and laboratory improvement. It is suggested that the pathology in papular mucinosis may include serious rheumatic manifestations in addition to the cutaneous involvement.