We will discuss the rationale and methodology of a proposed observational study of CIN3 in n=200 young women (CIN3MA). In 2018, the NZ cervical screening age will increase to 25 years. This will lead to a delay in the diagnosis and treatment of high grade cervical abnormalities in young women of up to 5 years. While screening in women aged 20-24 appears to have no effect on invasive cervical cancer rates, annually ~1100 NZ women in this age group are diagnosed with high grade cervical cell abnormalities (CIN2 and 3). Usually these women are treated and we have a poor understanding of the impact of deferred diagnosis on these lesions. There is evidence that a high proportion of CIN2 lesions naturally resolve in young women, but the impact of delayed CIN3 diagnosis and treatment in young women is poorly understood. Histological diagnosis for CIN3MA will be confirmed through multidisciplinary review and ki67 immunohistochemistry. Primary outcome measures of CIN3MA will be proportion of participants whose CIN3 lesions regress to CIN1 or less, who progress to invasion, who require treatment, and who are lost to follow up. Clinical and cytology/pathology predictors of outcome will also be investigated (e.g., HPV genotype, smoking, lesion size, immunohistochemical markers). We will also report on the changing epidemiology of HPV-related CIN3 in the post-vaccination era. We hypothesise that CIN3 observational management can be safely performed for women aged <25 years in a multicentre trial and a significant proportion will regress.