Pulmonary artery aneurysm (PAA) is a common finding in patients with long-term pulmonary arterial hypertension (PAH). The influence of PAH severity in the development of PAA remains unclear. We sought to determine whether PAA development is related to PAH severity and whether treatment optimization based on risk profile estimation is effective to stop pulmonary artery (PA) enlargement. This is a retrospective study of 125 PAH patients who underwent an imaging test (computed tomography or magnetic resonance) combined with a right heart catheterization within a six-month period. A multivariate analysis was performed to identify independent risk factors for PAA. Patients who underwent an additional imaging-test and RHC during follow-up were analyzed to evaluate changes on PA dimensions. PAA was diagnosed in 42 (34%) patients. PAA was more frequent in patients with congenital heart disease and toxic oil syndrome. PAH time-course showed to be an independent risk factor for PAA (HR 1.051, 95% CI 1.013–1.091, p = 0.008) whereas PAH severity did not. Twenty-six patients underwent a follow-up imaging-test and catheterization. After treatment optimization, a non-significant reduction of mean PA pressure was observed (58.5 mmHg [43.5–70.8] vs. 55.5 mmHg [47.5–66.3], p = 0.115) and a higher proportion of patients achieved a low-risk profile (19% vs. 35%, p = 0.157). However, the PA diameter significantly increased (40.4 ± 10.1 mm vs. 42.1 ± 9.6 mm; p = 0.003). PAA is a common condition in long-standing PAH but its development is not necessarily related to PAH severity. Despite stabilization after treatment optimization, a progressive PA dilatation was observed.