Despite size and relevance of non-adherence to health treatments, robust evidence on its effects on health care utilisation is very limited. We focus on non-adherence to diabetes treatments, a widespread problem, and employ longitudinal administrative data from Spain (2004-2010) to identify and quantify the effects of uncontrolled type 2 diabetes on health care utilisation. We use a biomarker (glycated haemoglobin, HbA1c) to detect the presence of uncontrolled diabetes and explore its effects on both primary and secondary health care. We estimate a range of panel count data models, including negative binomials with random effects, dynamic and hurdle specifications to account for unobserved heterogeneity, previous utilisation and selection. We find uncontrolled diabetes in around 30% of patients of both genders. Although women appear to systematically consume more health care compared to men, their consumption levels do not appear to be influenced by uncontrolled diabetes. Conversely, among men uncontrolled diabetes increases the average number of GP visits per year by around 4%, specialist visits by 4.4% and greatly extends hospital length of stay.