Adenoid cystic carcinoma is a rare epithelial tumour, and comprises about 1% of all malignant tumours of the oral and maxillofacial region. It is a malignant tumour which may develop in the trachea, bronchus, lungs or mammary glands, in addition to the head and neck region. Occurrences in the head and neck are mostly detected in the major salivary gland, oral cavity, pharynx and paranasal sinus where it presents as a slow growing firm nodular swelling. The aim of the article is to highlight the unique presentation of adenoid cystic carcinoma as a solitary ulcer on the floor of the mouth.