12 cases of acinic cell carcinoma diagnosed in Northern Ireland from 1942 to 1982 on which there was at least 10 years' follow-up were reviewed, by pooling cases from all regional pathology laboratories. Clinical findings at presentation were established from case notes, together with details of eventual clinical outcome. Sections were examined to determine tumour size, morphological pattern and cytological constitution, the presence or absence of cytological atypia, mitotic activity, lymphocytic and desmoplastic responses, and to assess for infiltrative margins and adequacy of excision. The tumours arose in 8 females and 4 males, aged 22 to 86 years at presentation. Eleven tumours were in the parotid, one in the soft palate. Two patients suffered local recurrence, both more than 7 years after diagnosis. Five patients had regional lymph node metastasis, four at presentation. No patient suffered haematogenous metastasis or died of tumour. Of the features examined, incomplete excision increased the risk of local recurrence. While numbers are small, the acinic cell carcinoma in Northern Ireland is an unpredictable low-grade malignant tumour which is capable of recurrence and metastasis. Adequate excision at presentation appears to be the most appropriate therapy.