OBJECTIVES: The management of SI in patients at high CV risk is poorly understood within Canada. The present study was conducted to describe SI patient characteristics and their management and to estimate the incidence in the high-risk population. METHODS: We retrospectively analysed data from an open cohort of patients initiating statin therapy between 2004 and 2012, using the Southwestern Ontario primary-care practice database. Inclusion criteria were: diagnosis of dyslipidaemia, ≥1 statin prescription, and ≥2 years of statin-free baseline data. SI index date was identified as the first occurrence of SI-related symptoms associated with a change in statin therapy. Patients were stratified into three CV risk levels (low, intermediate, high). Here, we report results for the high-risk subgroup. RESULTS: Of 41,733 patients who initiated statin therapy, 14,607 were at high CV risk; 1,294 patients in this subgroup had SI. The mean±SD age was 61±8.9 years, 53% (n=684) were male, and low-density lipoprotein cholesterol (LDL-C) was 2.8±1.1 mmol/L. Among patients identified with SI, 13% (n=170) experienced myopathy and 87% (n=1124) had SI-related symptoms. There were nine rhabdomyolysis cases, two resulting in hospitalization. Statins were discontinued in 412 (32%) patients, and 677 (52%) patients had their statin dosage decreased. At the SI index date 84% (n=1085) of patients were on LDL-C target, with the on-target proportion decreasing to 49% (n=638) 6 months post-SI. Among the 656 patients off-target at 6 months post-SI, 28% (n=185) decreased statin dose or stopped statins, and 46% (n=299) were switched to a non-statin therapy. CONCLUSIONS: SI affects the optimal treatment of dyslipidaemia in this high-risk population. A number of patients do not achieve their LDL-C target and are undertreated because they do not tolerate their initial statin dose or have to be treated with a non-statin therapy. These patients are at increased CV risk.