Background: Combination drug therapy for pulmonary arterial hypertension (PAH) is the international standard of care for most patients, however in Australia there are barriers to drug access. This study evaluates current treatment of PAH patients in Australia and the consistency of therapy with international guidelines. Methods: Cross-sectional analysis of patients with Group 1 PAH enrolled in the Pulmonary Hypertension Society of Australia and New Zealand Registry (PHSANZ) at 31 December 2017. Drug treatment was classified as monotherapy or combination therapy and adequacy of treatment was determined by risk status assessment using the Registry to Evaluate Early and Long-Term PAH Disease Management (REVEAL) 2.0 risk calculator. Predictors of monotherapy were assessed using a generalised linear model with Poisson distribution and logarithmic link function. Results: 1,046 patients met the criteria for analysis. Treatment was classified as monotherapy in 536 (51%) and combination therapy in 510 (49%) cases. Based on REVEAL 2.0, 184 (34%) patients on monotherapy failed to meet low-risk criteria and should be considered inadequately treated. Independent predictors of monotherapy included age greater than 60 years (risk ratio [RR] 1.23, 95% confidence interval [CI] 1.09–1.38; p=0.001), prevalent enrolment in the registry (RR 1.21 [95%CI 1.08–1.36]; p=0.001) and comorbid systemic hypertension (RR 1.17 [95%CI 1.03–1.32]; p=0.014), while idiopathic/heritable/drug-induced PAH subtype (RR 0.85 [95%CI 0.76–0.96]; p=0.006), functional class IV (RR 0.50 [95%CI 0.29–0.86]; p=0.012), increased right ventricular systolic pressure (RR 0.99 [95%CI 0.99–1.00]; p<0.001) and increased pulmonary vascular resistance (RR 0.96 [95%CI 0.95–0.98]; p<0.001) were less likely to be associated with monotherapy. Conclusions: Most Australian PAH patients are treated with monotherapy and a significant proportion remain at risk of poor outcomes. This is below the standard of care recommended by international guidelines and at risk patients should be escalated to combination therapy.