Cerebral microbleeds (CMBs) reflect an underlying angiopathy currently thought to result mainly from hypertension or from the deposition of beta-amyloid in small and micro vessel walls. This chapter describes the prevalence of, and risk factors for, CMBs and methodological issues related to their study. CMBs can be present in up to 80% of a clinical hemorrhagic stroke sample. Most studies with a reasonable distribution of subject age and sample size show CMB prevalence increases with age. There is robust evidence that high blood pressure, measured in different ways, is a risk factor for CMB. Most genetic diseases with increased susceptibility to CMBs are rare. The only candidate susceptibility gene identified as risk modifying is APOE. Research on risk factors for CMBs will bring into better focus issues related to comorbidity with other vascular and neurodegenerative lesions and location and number of lesions.