High blood pressure (BP) is highly prevalent among the elderly, and even with pharmacological therapy BP is difficult to control to guideline recommended levels. Although poor compliance to therapy is associated with less BP control, little is known regarding other barriers to attaining on-treatment target BP. This study examined factors associated with achieving on-treatment target BP in 6010 hypertensive participants aged 65-84 years from the Second Australian National Blood Pressure study. Participants were followed for a median of 4.1 years, with BP monitored every 6 months. 'Target BP' was defined as a reduction of systolic/diastolic BP of at least 20/10 mm Hg and BP <160/90 mm Hg from randomization in two consecutive follow-up visits. Cox regression was used to identify factors associated with achieving target BP from a number of baseline and in-study factors. Mean BP at randomization was 168/91 mm Hg and patients had a median of 9 (range: 2-20) study visits. Target BP was achieved in 50% of patients. Demographic factors associated with achieving target BP were male gender, living in a regional area; and clinical factors included history of antihypertensive therapy, increased plasma creatinine, lower pretreatment pulse pressure and in-study use of multiple BP-lowering drugs. Those aged >80 years and seeking care from multiple doctors (hazard ratio 0.40, 95% confidence interval 0.36-0.45, P<0.001) were less likely to achieve target BP. These findings identify clinical markers that can be targeted for intervention, but also demographic factors related to service delivery, which may provide further opportunity for achieving better BP control in hypertensive elderly.