Identifying and refining small-animal models of tuberculosis that recapitulate aspects of human Mycobacterium tuberculosis infection can contribute to advancing our understanding of critical facets of the disease. To study the effects of very low-dose infections with 2 strains of M. tuberculosis on disease progression and survival in common marmosets, animals were challenged with strains Erdman and CDC1551 at doses ranging from 1 to 12 cfu. These data revealed that the susceptibility of marmosets to M. tuberculosis infection is influenced by strain virulence and initial dose. Marmoset infection with the Erdman strain, even at very low doses, resulted in rapid disease progression associated with severe weight loss, extensive pathology, and poor survival. By contrast, challenge with the less virulent CDC1551 strain resulted in slower disease progression, delayed weight loss, and prolonged survival. One marmoset infected with CDC1551 at a very low dose (approximately 1 cfu) was able to contain and control M. tuberculosis infection in a subclinical state that persisted as long as 300 d. These findings underscore the critical importance of understanding the heterogeneity in host outcome that can arise in association with different infectious doses and strains in the marmoset model of tuberculosis.