Background: Iloprost is a stable prostacyclin analogue that is associated with a longer duration of vasodilatation and has been approved for inhalative use with 6 or 9 inhalations during the daytime and a night pause. It is not known if during the night pause rebound pulmonary hypertension occurs. The aim of this study was to assess the hemodynamics in iloprost-treated patients during the daytime and at night. Methods: We enrolled 5 adult patients (aged 45 ± 10 years) with idiopathic pulmonary arterial hypertension (IPAH) and chronic inhaled iloprost therapy for at least 12 months. Further medication remained unchanged during the study period. Hemodynamics were monitored by right heart catheterization. Results: After 30–60 min of nebulized iloprost, mean pulmonary arterial pressures (PAP) decreased from 68 ± 15 to 51 ± 18 mm Hg (p = 0.004). After 6 h off-medication sleeping time, mean PAP initially increased until 2 a.m. and decreased subsequently until wake-up time at 6 a.m. Mean PAP, cardiac index and pulmonary vascular resistance at night were not significantly different from the values during the day. Conclusions: In this study, patients with IPAH and chronic nebulized iloprost therapy did not reveal a rebound pulmonary hypertension during off-medication sleeping time.