Aim CT imaging is increasingly used in the pre-operative localisation of abnormal parathyroid glands. Parathyroid glands typically enhance in the arterial phase and washout in the delayed phase. The aim of this novel study was to analyse and classify all various enhancement patterns. Method 42 patients underwent a three-phase CT which identified 45 abnormal glands all of which subsequently had surgical excision and histological assessment. The Houndsfield Units (HU) in the 45 glands was compared with that of an area of normal adjacent thyroid in the three phases and classified as below: Results 45 glands were surgically removed, 37 were adenomas and 8 hyperplastic on histology. The adenomas were classified as follows: type A (48.7%), type B (5.4%), type C (43.2%) and type D (2.7%). Hyperplastic glands were classified as type A (37.5%) and type B (62.5%). Conclusion Traditionally type A is the prevalent enhancement pattern, yet several other patterns of enhancement are observed in this study which vary between adenomatous and hyperplastic glands. Clinician awareness of this is important and lack of typical enhancement should not be used in isolation to exclude an abnormal parathyroid gland.