One of the primary challenges encountered in managing captive callitrichids is a group of gastrointestinal disorders that are collectively known as Marmoset Wasting Syndrome (MWS). Unfortunately, MWS is still not well understood. It is suggested that MWS has a multifactorial etiology; stress, infection, malnutrition, malabsorption, and enteritis or colitis may be associated with MWS. Usually, animals demonstrate more than one of the following clinical signs: progressive weight loss, alopecia, chronic diarrhea, muscle atrophy, hypoproteinemia, and anemia. Recent advances in diagnostics, mostly noninvasive fecal and urine tests, yielded promising results. Good treatment results have been achieved with the administration of glucocorticoids and tranexamic acid, although no cure has been found yet. Probiotics and gel diets also demonstrated to be potentially useful. However, once animals are affected by MWS, treatments eventually become ineffective, and animals will inevitably require euthanasia to prevent further suffering. Preventative measures should be aimed at reducing stress and optimizing housing, husbandry, and diets. More research is warranted to elucidate the pathogenesis of MWS in captive callitrichids and to refine diagnostic and treatment methods.