Gender-based violence (GBV) is a pervasive issue in Tanzanian slums, affecting women disproportionately. Counseling centers have emerged as critical interventions to address GBV, yet their effectiveness remains under-researched. A mixed-methods approach involving pre- and post-intervention surveys, focus group discussions, and qualitative interviews was employed to gather data from survivors and service providers. Data analysis included descriptive statistics and thematic content analysis. Survivors reported a significant decrease in GBV incidents following their enrollment in counseling centers (75% reduction), with themes of improved emotional support and increased confidence among participants. Counseling centers have played a crucial role in supporting survivors, but further interventions are needed to ensure sustained impact over time. Recommendations include expanding coverage and enhancing service quality to reach more vulnerable populations. Expand the number of counseling centers in underserved areas, enhance training programmes for counselors, and integrate GBV prevention strategies into broader community development initiatives. Gender-Based Violence Counseling Centers, Tanzanian Slums, Longitudinal Impact Assessment