Ninety-seven patients with light chain disease (LCD) were studied. The median survival from diagnosis was 30 mo for 52 patients with kappa-LCD and 10 mo for 45 patients with lambda-LCD (p less than 0.0007). A lower proportion of kappa-LCD patients (15.7%) than lambda-LCD patients (42.2%) died within the first 6 mo after diagnosis. The survival of the remaining patients with kappa-LCD was still much longer than of those with lambda-LCD (p = 0.022). The shorter survival of lambda-LCD patients could not be ascribed to an increased incidence of recognized manifestations indicating a poor prognosis (e.g., anemia, hypercalcemia, azotemia, low albumin, the extent of osteolytic lesions, or proteinuria), the incidence of amyloidosis, the clinical stage of the disease at diagnosis, or the response to treatment, and remains unexplained. A comparison of the clinical manifestations of LCD with those of other myelomas revealed some differences. LCD patients were slightly younger than IgA and IgG patients but older than IgD patients. A 1:1 ratio of males to females was similar to the ratios in IgA and IgG myeloma, but differed from the 3:1 ratio reported for IgD myeloma. Plasma-cell leukemia developed in 7/97 LCD patients, an incidence that was higher than has been reported in other myelomas. The initial BUN was more than or equal to 30 mg/100 ml in 54 of 95 LCD patients, an incidence that was higher than has been reported for IgA and IgG myeloma, but lower than the incidence in IgD myeloma. The incidence of amyloidosis in LCD (23 of 97 patients) was similar to that reported for IgA and IgG myeloma, but less than the incidence in IgD myeloma.