Abstract Gastrointestinal parasites are a major clinical and economical threat to New World camelids (NWC) throughout the world. Since there are no anthelmintics approved for use in NWC, there is only limited information about the efficacy and safety of these products. In this study, the reduction of the faecal egg output following treatment with an injectable formulation of ivermectin in NWC was evaluated. Therefore, a group of 10 llamas and a group of eight alpacas, naturally infested with Trichostrongylus spp. and Oesophagostomum spp., were randomly divided into a treated and a control group, and injected with ivermectin subcutaneously at a dose rate of 0.2 mg/kg bodyweight. Faecal samples were collected per rectum immediately prior to treatment from each individual animal in the study, and every week thereafter for the next 5 weeks. Both for the llamas and the alpacas, there was a 100% reduction in faecal egg output during at least 3 weeks. None of the animals showed adverse reactions to the ivermectin treatment.