Functional and anatomic characteristics of patent foramen ovale (PFO) were investigated in 66 professional scuba divers (41 with and 25 without decompression illness) using transthoracic and transesophageal echocardiography. PFO with right-to-left shunting at rest is associated with decompression illness, particularly the neurologic type. A wider patency diameter together with a higher membrane mobility are associated with the risk of developing the disease in divers with PFO.