Purpose: To compare urinary levels of monocyte chemoattractant protein-1 (MCP-1), an inflammatory cytokine, in healthy controls and overactive bladder (OAB) patients, to correlate changes in urinary MCP-1 with OAB treatment response and symptom severity, and to study the diagnostic potential of MCP-1 for OAB, as well as the efficacy of MCP-1 as a potential biomarker for different phenotypes of OAB. Methods: We used enzyme-linked immunosorbent assay to measure normalized urinary MCP-1 levels in 56 individuals (43 OAB patients and 13 controls). We assessed the OAB patients at 3 visits with 2 validated symptom severity questionnaires (OAB-V8 and Patient Perception of Bladder Condition). Results: The mean pretreatment urinary MCP-1 level at visit 1 (229.2-pg/mg creatinine) was significantly greater than the MCP-1 levels at visit 3 in both the treatment (107.0-pg/mg creatinine) (P<0.001) and control (52.35-pg/mg creatinine) groups (P<0.001). Average OAB symptom severity decreased significantly from visit 1 (baseline) to visits 2 (4 weeks) and 3 (12–14 weeks) and was significantly correlated with urinary MCP-1 levels. Urinary MCP-1 levels dropped significantly (P=0.002) posttreatment in patients whose symptom severity improved by >30%, whereas nonresponders displayed no significant MCP-1 decrease (P=0.164). The receiver operating characteristic analysis of the OAB visit 1 and control groups produced an area under the curve of 0.891. We found no significant differences in sex, race, or age between the OAB and control groups. Conclusions MCP-1 levels differed significantly between the control and OAB groups and were closely correlated with symptom severity and treatment response. The good diagnostic accuracy of MCP-1 for OAB suggests the potential usage of MCP-1 for OAB diagnosis. The varying response of urinary MCP-1 levels to treatment may indicate at least 2 potential phenotypes of OAB. MCP-1, in combination with other biomarkers and symptom severity questionnaires, could potentially aid in developing a patient-centered OAB treatment approach.