A survey of whipworms was conducted in llamas and vicuñas in northwestern Argentina. Fecal examinations of a group of 14 llamas (April 1995-March 1996) and 69 vicuñas (November 1996) indicated a high prevalence (usually >50%) of Trichuris sp. in these hosts. Prevalence was highest during July-November 1995 that also coincided with the highest mean fecal egg count. During postmortem examinations of 1 llama and 1 vicuña, specimens of Trichuris tenuis were recovered from the cecum/large intestine of each camelid. This is the first report of T. tenuis in South America, and the first report in the vicuña. It is suggested that T. tenuis is the typical whipworm of aboriginal camelids.