Background Adenoid cystic carcinoma (ACC) is a rare malignancy arising from salivary glands, accounting for around 1% of head and neck cancers. Sublingual gland ACC is exceptionally uncommon, comprising only about 0.3–1% of all salivary gland tumors. ACC can present as a subtle, benign-appearing submucosal lump, making early diagnosis challenging leading to delayed recognition. Case A 34-year-old man with a firm submucosal mass in the left floor of mouth. The lesion appeared well-defined on exam. Initial excision of the sublingual gland mass unexpectedly revealed T3 ACC on histology with close margin. Definitive surgery entailed a wide local re-excision of the floor of mouth with 1 cm margins and ipsilateral neck dissection. Final margins were clear, and the patient’s course was uncomplicated post-resection. One year oncosurveillance has been unremarkable. Discussion This case illustrates the diagnostic challenges of sublingual ACC. The tumor’s initial benign appearance and non-specific imaging demonstrated how ACC can mimic benign salivary lesions. This led to a limited initial excision. Given ACC’s tendency for perineural tracking and late recurrences, achieving clear margins and long-term surveillance are critical. Early re-excision in our patient prevented residual disease, and adjuvant therapy was considered due to the tumor’s aggressive biology. Reference: 1. Coca-Pelaz A, Rodrigo JP, Bradley PJ, Vander Poorten V, Triantafyllou A, Hunt JL, Strojan P, Rinaldo A, Haigentz Jr M, Takes RP, Mondin V. Adenoid cystic carcinoma of the head and neck–An update. Oral oncology. 2015 Jul 1;51(7):652-61. 2. Kumar VS, Prathi VS, Manne RK, Beeraka S, Natarajan K. Adenoid cystic carcinoma of sublingual salivary gland obstructing the submandibular salivary gland duct. Journal of Clinical Imaging Science. 2013 Oct 29;3(Suppl 1):10.