Background: Breast lesions present commonly as a lump(s) in the breast for which differentiation between benign and malignant lesions is often difficult using clinical examination alone. The standard practice in the management of a breast lump since the time of Halstead is by operative biopsy under anaesthesia and pathological evaluation of the biopsied tissue. Fine needle aspiration cytology (FNAC) has been established as a quick, simple and accurate alternative to open surgical biopsy. Objectives: This study was undertaken to describe the pattern of diagnosis made on FNAC of breast lesions at University College Hospital (UCH), Ibadan over a ten year period; to correlate the cytological and histological diagnosis of breast lesions over the same period and to compare the results of this study with the suggested thresholds for cytology performance recommended by the National Health Service Breast Screening Programme (NHSBSP) Guidelines of the United Kingdom (UK) and with similar work done previously in Ibadan and elsewhere. Methods: A retrospective evaluation of 1401 patients with breast lesions who had FNAC, of which 250 had histological confirmation. Results: Overwhelming majority (97%) of the aspirates was obtained from females with a mean age of 39.5 years. Fibroadenoma constitutes the bulk (32.4%) of benign breast smear category, while carcinomas constitute the bulk (97.3%) of the malignant breast smear category. Of the 125 histologically confirmed benign lesions, 115 had been interpreted as benign cytologically, while 3, 4, 1, and 2 cases respectively were reported as malignant, suspicious of malignancy, atypia probably benign and unsatisfactory. There were 125 histologically confirmed malignant cases, 93 of which had been reported as malignant on FNAC, 21 as suspicious of malignancy, 8 as benign and 3 as unsatisfactory. The positive predictive value for malignancy was 99.3% with a complete sensitivity of 97.7% and specificity (full) of 94.2%. Conclusion: The high quality assurance measures, which are well above the minimum standards recommended by the UK NHSBSP guideline for cytology, obtained in this relatively large sample sized retrospective study confirms FNAC as a clinically effective diagnostic procedure for breast lesions in University College Hospital, Ibadan and justifies its use as a first line diagnostic procedure in the evaluation of patients with breast lesion in this institution.