In 2008, a cholera outbreak with unusually high mortality occurred in western Kenya during civil unrest after disputed presidential elections. Through active case finding, we found a 200% increase in fatal cases and a 37% increase in surviving cases over passively reported cases; the case-fatality ratio increased from 5.5% to 11.4%. In conditional logistic regression of a matched case-control study of fatal versus non-fatal cholera infection, home antibiotic treatment (odds ratio [OR] 0.049; 95% CI: < 0.001-0.43), hospitalization (OR, 0.066; 95% CI, 0.001-0.54), treatment in government-operated health facilities (OR, 0.15; 95% CI, 0.015-0.73), and receiving education about cholera by health workers (OR, 0.19; 95% CI, 0.018-0.96) were protective against death. Among 13 hospitalized fatal cases, chart review showed inadequate intravenous and oral hydration and substantial staff and supply shortages at the time of admission. Cholera mortality was under-reported and very high, in part because of factors exacerbated by widespread post-election violence.