The clinical search for onchocercal nodules, and their preferred sites on the body in different geographic areas are described and illustrated. The differential diagnosis of onchocercomata is discussed and figures on the frequency of false diagnoses are reported. The prevalence of adult Onchocerca volvulus in relation to the endemicity of infection, the age and sex of the patients, the localisation of nodules on the body, and the measures used to control onchocerciasis are discussed. Recommendations are made on the selection of patients for different medical studies. The technique of nodulectomy and the equipment needed are described.