Pulmonary hypertension is a disease that is characterized by an increased pulmonary artery pressure and often results in right ventricular failure. Patients of any age might present with exertional dyspnea and fatigue, but clinical signs and symptoms can sometimes be difficult to recognize. Therefore, histopathology might become critical for the diagnosis. Pulmonary hypertension can be idiopathic, familial or associated with drugs/toxins or other diseases. Morphologic changes that lead to pulmonary hypertension can involve pulmonary arteries, veins and/or capillaries. Histopathologic findings might include medial hypertrophy, concentric laminar intimal fibrosis, plexiform lesions, dilatation lesions, fibrinoid necrosis and arteritis and thromboembolic lesions of pulmonary arteries, capillary proliferations and venous changes. Classification of pulmonary hypertension has changed over the years. Heath and Edwards (1958) originally classified pulmonary hypertension based on histopathologic findings in patients with congenital heart disease. The most recent classification, proposed at the 5th World Symposium on Pulmonary Hypertension (2013), groups categories that share similar pathologic and hemodynamic characteristics and management. Progress has been made in our understanding of the pathogenesis of the disease. We will discuss clinical findings, classification, histopathologic features and recent developments in pathology and pathogenesis of pulmonary hypertension. Pulmonary hypertension is a disease that is characterized by an increased pulmonary artery pressure and often results in right ventricular failure. Patients of any age might present with exertional dyspnea and fatigue, but clinical signs and symptoms can sometimes be difficult to recognize. Therefore, histopathology might become critical for the diagnosis. Pulmonary hypertension can be idiopathic, familial or associated with drugs/toxins or other diseases. Morphologic changes that lead to pulmonary hypertension can involve pulmonary arteries, veins and/or capillaries. Histopathologic findings might include medial hypertrophy, concentric laminar intimal fibrosis, plexiform lesions, dilatation lesions, fibrinoid necrosis and arteritis and thromboembolic lesions of pulmonary arteries, capillary proliferations and venous changes. Classification of pulmonary hypertension has changed over the years. Heath and Edwards (1958) originally classified pulmonary hypertension based on histopathologic findings in patients with congenital heart disease. The most recent classification, proposed at the 5th World Symposium on Pulmonary Hypertension (2013), groups categories that share similar pathologic and hemodynamic characteristics and management. Progress has been made in our understanding of the pathogenesis of the disease. We will discuss clinical findings, classification, histopathologic features and recent developments in pathology and pathogenesis of pulmonary hypertension.