This article reviews the prevalence, risk factors, natural history, and impact on quality of life of painful diabetic neuropathy (PDN) and postherpetic neuralgia (PHN). Diabetes mellitus afflicts more than 14 million persons in the U.S. An estimated 20% to 24% of these persons experience PDN. Data on risk factors for PDN are limited, but duration of diabetes mellitus and poor glycemic control are probably important factors. Painful diabetic neuropathy may interfere with general activity, mood, mobility, work, social relations, sleep, leisure activities, and enjoyment of life. Herpes zoster strikes an estimated 800,000 persons each year in the U.S., most of whom are elderly or immunosuppressed. Using pain at 3 months after rash onset as a definition of PHN, between 25% and 50% of adults older than 50 years develop PHN, depending on early antiviral therapy for herpes zoster. Increasing age, greater pain and rash severity, greater degree of sensory impairment, and psychological distress are risk factors for PHN. Postherpetic neuralgia may cause fatigue, insomnia, depression, anxiety, interference with social roles and leisure activity, and impaired basic and instrumental activities of daily living. Both conditions are common complications of their underlying disorders and can profoundly diminish the quality of life of affected persons.