Background: TP53 mutations are reported in 5% of patients with adenoid cystic carcinoma (ACC). Whilst TP53 mutations are associated with adverse clinical outcomes across multiple tumour types, their prognostic significance in ACC is unknown. We sought to determine the utility of TP53 mutations as a prognostic biomarker in a prospective cohort of ACC patients. Methods: From April 2017 to September 2019, 146 patients with ACC were prospectively recruited to an ethically approved study. DNA was extracted from archival FFPE samples and underwent targeted next generation sequencing (Qiagen GeneRead DNAseq Targeted Panel V2 n = 134; Foundation Medicine; n = 12). Clinical, pathological and outcome data were collected on all patients and Kaplan-Meier survival analysis was performed to test for survival differences between TP53 mutated and wild-type ACC. Results: 146 ACC patients (mean age 48 years, range 16-79) underwent DNA extraction and next generation sequencing for TP53 mutations. The primary site was major salivary gland in 47% and minor salivary gland in 48% (other 5%). Analysis was successful in 122/146 patients (84%). Recurrent or metastatic disease was present in 94% (115/122) at study entry. TP53 alterations were identified in 9% (11/122), most frequently within the DNA binding domain (9/11). Non-pulmonary visceral metastases were seen more frequently in TP53 wild-type than in TP53 mutated ACC (44% vs. 10%; p = 0.042), and other clinical parameters were balanced between groups. During follow-up from diagnosis (median follow up 6.6 years), death occurred in 45% of patients with TP53 mutation and in 23% with TP53 wild-type ACC (p = ns). In TP53 mutated ACC, median overall survival was significantly shorter (5.3 vs. 16.3 years), and 10-year survival rate significantly lower (42% vs. 82%) than TP53 wild-type ACC (log-rank p = 0.013). Conclusions: In this cohort of patients with ACC, TP53 mutations were seen with a higher frequency than previously reported. This may be explained by the high frequency of recurrent or metastatic disease at study entry. TP53 mutation was associated with a statistically significant reduction in overall survival in patients with recurrent and metastatic ACC. These findings suggest that stratifying by TP53 status may be of clinical value to inform follow-up strategy in addition to established clinical, pathological and genomic biomarkers.