BACKGROUND. Classic Kaposi sarcoma (CKS) is an inflammatory-mediated neoplasm that develops in the presence of KS-associated herpesvirus (KSHV) and immune perturbation. In the current study, the authors compared CKS cases with age-matched and sex-matched KSHV-seropositive controls without human immunodeficiency virus-1 infection and markers of viral control, blood counts, CD4-positive and CD8-positive lymphocytes, and serum β-2-microglobulin and neopterin levels. METHODS. Viral loads were detected using real-time amplification of the KSHV-K6 and EBV-pol genes, anti-K8.1 (lytic) titers were detected by enzyme-linked immunoadsorbent assay, and antilatent nuclear antigen (LANA) titers were detected using immunofluorescence. Odds ratios (OR) and 95% confidence intervals (95% CI) were calculated using logistic regression adjusted for sex, age, and study site. RESULTS. Peripheral blood mononuclear cells (PBMC) KSHV DNA detection (P ≤ .0001) and high KSHV lytic (>1:1745; P ≤ .0001) and latent (>1:102,400; P = .03) antibody titers were found to be positively associated with CKS risk. Antibody titers were higher in cases with lesions compared with cases without lesions (P ≤ .05). The detection of Epstein-Barr virus (EBV) DNA in PBMCs was not found to be associated with CKS (P = .95). Independent of PBMC KSHV DNA, CKS risk was found to be positively associated with reduced hematocrit (<37.4%; P = .03), hemoglobin (<12g/dL; P = .04), and lymphocytes (<1000 cells/μL; P = .004), including CD4-positive (+) cells (<457 cells/μL; P = .07) and CD8+ cells (<213cells/μL; P = .04), and with increased monocytes (≥638 cells/μL; P = .009). Nonsignificant elevations of β-2-microglobulin and neopterin were observed among cases regardless of disease burden (P ≥ .08). In a multivariate model, the CKS risk was found to be associated with PBMC KSHV DNA (OR of 2.7; 95% CI, 1.4-5.3), a high KSHV lytic antibody titer (OR of 3.7; 95% CI, 1.9-7.4), and low lymphocytes, particularly among those patients age <70 years (OR of 8.0; 95% CI, 2.7-23.7). CONCLUSIONS. The findings of the current study appear to corroborate the specificity of KSHV and highlight the hematologic and immunologic correlates involved in the pathogenesis of CKS.