Even if the crucial role of microvascular disease has been widely explored in the acute phase of COVID-19, little is known about the relevance of this mechanism of lung injury during convalescence. The simultaneous measurements of DL_NO and DL_CO allows the sub-categorization of both vascular (Vc) and membrane components (Dm) of lung diffusing capacity. In this paper we explore the changes in DL_NO and DL_CO as an assessment of the microvascular damage underling COVID-19 pulmonary sequelae. We included 199 adult patients divided in four groups for COVID-19 severity (mild, moderate, severe and critical). We obtained pulmonary function tests and comprehensive medical evaluation at 4 months post discharge. DL_CO and DL_NO impairment were respectively observed in 111 (56%) vs 167 patients (84%). Overall, DL_NO appeared more compromised compared to DL_CO, with a median value of 49.4% (40.2 ? 61.3) vs 69.2% (53.4 ? 83.3). DLCO impairment was higher in severe and critical groups (p=0.001), but no difference was observed in DLNO values. Median DL_NO/DL_CO ratio was 3.75 (3.42 ? 4.18) and resulted significantly higher in critical group compared to the other sub-groups of hospitalised patients (4,08 vs 3.57, p< 0.001). Vc (%), was significantly reduced in critical disease compared to mild and moderate (60.1 vs 87.1 and 79.6 respectively, p=0.005), while no difference was observed in Dm (%). In the multiple regression model, critical disease and lower PaO2/FiO2 ratio were associated with a higher DL_NO/DL_CO ratio (p = 0.007 and p = 0.0012). Our data confirm that patients discharged after severe or critical COVID-19 have a higher amount of microvascular disease.