Background and Objectives: Naevi may change in size, shape and colour due to multiple inherent and external factors. We observed naevi changing size in adults at high risk of melanoma, and assessed associations of change with demographic factors, skin type, sites of naevi and history of melanoma. Methods: In total, 29 participants with a personal or first-degree family history of melanoma or those deemed at high risk with multiple naevi of variable morphologies had all melanocytic naevi 0.5-1cm imaged and their maximum diameter recorded. Maximum diameters from repeat imaging of naevi 12 months later were compared to baseline measurements. Newly appearing naevi ≥5mm and naevi that grew or decreased in size by 20% or more were defined as changeable naevi. Associations between changeable naevi and participants' age, sex, skin type, body sites of naevi and personal and family history of melanoma were assessed. Results: There was no difference in changeable naevus rates among sex, age or skin type. Among the body sites, the head and neck were most likely to have changeable naevi, and the upper limbs the least likely. A family history of melanoma almost tripled the likelihood of having changeable naevi compared with those without both personal and family melanoma history. Conclusions: Naevi can continue to change in size throughout adulthood, showing both increases and decreases in size as well as the appearance of new naevi. This has important clinical implications, in particular for sequential body imaging used for the detection of melanoma.