There is great interest in tumor stem cells (TSCs) as potential therapeutic targets; however, cancer therapies targeting TSCs are limited. A drawback is that TSC markers are often shared by normal stem cells (NSCs)^,,,; thus, therapies that target these markers may cause severe injury to normal tissues. To identify a potential TSC-specific marker, we focused on doublecortin-like kinase 1 (Dclk1). Dclk1 was reported as a candidate NSC marker in the gut^,, but recent reports have implicated it as a marker of differentiated cells (for example, Tuft cells)^,. Using lineage-tracing experiments, we show here that Dclk1 does not mark NSCs in the intestine but instead marks TSCs that continuously produce tumor progeny in the polyps of Apc^Min/+ mice. Specific ablation of Dclk1-positive TSCs resulted in a marked regression of polyps without apparent damage to the normal intestine. Our data suggest the potential for developing a therapy for colorectal cancer based on targeting Dclk1-positive TSCs.