The oral cavity is one of the most frequently affected sites by cGVHD following allogeneic hematopoietic cell transplantation (alloHCT), and can be a significant source of patient morbidity due to both mucosal and salivary gland involvement. The development of dental decay is a potentially devastating oral complication that has only rarely been reported in the transplantation literature. The purpose of this study was to comprehensively characterize a cohort of patients with cGVHD that subsequently developed extensive dental caries. A retrospective case-record review was conducted for patients who had undergone alloHCT at Dana-Farber/Brigham and Women's Cancer Center between 1990 and 2010 and developed cGVHD-associated rampant dental decay. All patients underwent dental evaluations before and after alloHCT that consisted of a soft and hard tissue examination and dental radiographs. Caries diagnosed from the pre-alloHCT evaluation were treated definitively such that all patients were considered free of caries at the time of admission for HCT. A total of 21 patients were identified with a median time of cGVHD onset of 5.4 months (range 2.2-18.5) post-alloHCT. All patients were diagnosed with oral cGVHD, with 90% demonstrating mucosal involvement, and 95% with salivary gland involvement. Post-alloHCT dental evaluation was performed at a median of 22 months (range 4-81) after alloHCT. when ten patients were diagnosed with gross caries and eight patients presented four or more affected teeth. Cervical and interproximal patterns of dental caries were frequently diagnosed. The proportion of patients with gross, one surface, and greater than one surface caries, categorized as 0, 1-3, or ≥4, were significantly higher post-alloHCT compared to pre-alloHCT with at least 50% of patients experiencing an increase. Patients with oral cGVHD, who were free of caries at the time of transplantation, developed extensive areas of cervical decay in a median time of less than two years post-alloHCT. This is the first comprehensive characterization of this severe late complication of alloHCT and oral cGVHD. Greater awareness on the part of transplant oncologists and dentists as well as more aggressive preventive measures are warranted, as well as prospective studies to better elucidate the incidence of this complication, identify risk factors, and evaluate the effectiveness of preventive interventions.