Objective Polyclonal hypergammaglobulinemia (PHGG) is a classic problem in internal medicine; however, its conditions and diagnostic procedures have not been well studied. We therefore conducted a retrospective study to characterize the PHGG disease spectrum. Methods We included all patients who underwent serum protein electrophoresis (SPEP) at a hematology tertiary referral center during a five-year period. For these patients, globulin clonality was determined and clinical data were extracted from the records. Results Out of 209 consecutive cases of hypergammaglobulinemia demonstrated by SPEP, 79 cases of PHGG were identified. A total of 46 diagnoses were associated with PHGG. Patients with PHGG were younger [median 71.0 years old (yo) vs. 65 yo; p=0.002] and had lower gamma-globulin levels (median, 26.5 g/L vs. 24.8 g/L; p=0.03) than those with monoclonal hypergammaglobulinemia. Interestingly, out of 79 patients with PHGG, 15 were associated with more than one diagnosis, and a female predominance was observed in this specific subset of patients. PHGG cases with multiple diseases showed higher gamma-globulin levels than those with monoclonal hypergammaglobulinemia, in a disease-dependent manner. Additionally, positive anti-nuclear antibodies (ANAs) had a discriminative ability with an area under the curve of 0.81 (95% confidence interval, 0.65-0.96) and were highly sensitive to multimorbidity in PHGG (sensitivity, 92.3%). Conclusion These results establish a previously underappreciated unique immunological state of multimorbidity in PHGG and indicate that the gamma-globulin levels and ANAs could serve as markers for the clinical assessment of comorbidities in PHGG.