A case of mastoid dermoid cyst (DC) was presented, and differences with cases of other temporal bone DCs were analyzed. The mastoid DC was also compared with mastoid congenital cholesteatoma. We reported a case of a patient with mastoid DC, evaluating her clinical, radiological, and surgical findings. A review of the literature was performed to compare our findings with those reported. The preoperative radiological evaluation prompted us to plan a surgical approach to the lesion, suspecting the presence of a mastoid congenital cholesteatoma. The surgical findings were in line with the presence of a mastoid DC. Only two cases reported in the literature presented features that fulfilled the criteria of a true mastoid DC. A DC confined to the mastoid region is an extremely rare clinical entity, with asymptomatic and slow growth. Preoperative radiological differentiation between congenital cholesteatoma and DCs with atypical features can be difficult. However, surgical excision is the treatment of choice in both cases. Diagnosis is confirmed by the histological evaluation. Cite this article as: Pepe G, Canzano F, Piccinini S, Corcione L, Falcioni M. Mastoid Dermoid Cyst. J Int Adv Otol 2020; 16(3): 473-5.