Background: Guidelines for limited-stage human immunodeficiency virus-associated Kaposi sarcoma (AIDS/KS) recommend antiretroviral therapy (ART) as initial treatment. However, many such individuals show worsening KS and require additional chemotherapy. Methods to identify such patients are lacking. Setting: We studied whether serum levels of biomarkers associated with angiogenesis, systemic inflammation, and immune activation, which are elevated in HIV-infected individuals and implicated in the development of KS, could prospectively identify individuals with limited-stage AIDS-KS who would benefit from chemotherapy administered with ART. Methods: Serum specimens were obtained from participants in a randomized trial evaluating the value of adding oral etoposide chemotherapy to ART in treatment-naïve people with limited-stage AIDS-KS in resource-limited settings. Serum biomarkers of inflammation (C-reactive protein [CRP], interleukin [IL]-6, IL-8, IL-10, granulocyte colony stimulating factor, soluble tumor necrosis factor receptor-2), immune system activation (soluble IL-2 receptor alfa, C-X-C motif chemokine ligand 10/interferon gamma-induced protein 10, C-C motif ligand 2/monocyte chemoattractant protein 1), and angiogenesis (vascular endothelial growth factor, matrix metalloproteinase-2, -9, endoglin, hepatocyte growth factor) were measured at entry to determine whether baseline levels are associated with KS response. On-treatment changes in biomarker levels were determined to assess how etoposide modifies the effects of ART. Results: Pretreatment CRP and IL-10 were higher in those whose KS progressed, and lowest in those who had good clinical responses. Pretreatment CRP, IL-6, and soluble tumor necrosis factor receptor-2 showed significant associations with KS progression at the week-48 primary endpoint. Immediate etoposide led to lower inflammation biomarker levels compared with ART alone. Early KS progression was associated with elevated pretreatment levels of inflammation-associated biomarkers and increasing levels post-treatment. Conclusions: Quantifying serum biomarkers, especially CRP, may help identify persons with AIDS-KS who would benefit from early introduction of chemotherapy in addition to ART. Trial registration: ClinicalTrials.gov NCT01352117.