Common marmosets (Callithrix jacchus) can sometimes be seen in general practice and it is essential to be aware of their nutritional, environmental and medical requirements. The keeping of common marmosets as pets is not recommended; they can be aggressive and unpredictable, and many are subjected to suboptimal husbandry. They are social species with psychological needs and good welfare is often difficult to achieve. This article summarises the basic care of common marmosets, discusses the approach to veterinary care, and highlights some important diseases that the clinician may see.