Four autopsy cases are presented in which sudden death was the initial manifestation of primary pulmonary hypertension. The arteriopathy was plexogenic in two cases (a 3-year-old girl and a 16-year-old boy) and was thrombotic in two other cases (55- and 59-year-old women). The diagnosis of primary pulmonary hypertension, particularly in forensic cases, requires that the pathologist be especially aware of the possibility and that a careful evaluation of multiple sections of lung be performed. Determination of the histopathologic type also is important because some forms of the disease may be familial and may be treatable in other family members if they are detected early.