To describe symptoms, surgical diagnosis and treatment, and long-term outcome of patients with symptomatic diaphragmatic endometriosis. Observational follow-up study. American tertiary referral center for the surgical treatment of endometriosis. Eight patients with diaphragmatic endometriosis causing severe or disabling symptoms. Laparoscopic diagnosis of diaphragmatic endometriosis followed by upper abdominal laparotomy for full-thickness resection of the diaphragm. Reduction of several symptoms as measured on a 5-point ranked ordinal scale administered by a phone survey up to 7 years after surgery. Laparoscopy from an umbilical port may identify small "sentinel lesions" of endometriosis on the anterior or mid diaphragm. Eight symptomatic patients all had significant invasive disease with dimensions up to 5 cm across of the posterior right diaphragm, which could not always be seen from the umbilical port site. All such lesions can be seen by a laparoscope placed beneath the right costal margin. Laparoscopic treatment of symptomatic disease is not rational given the posterior placement of the disease out of sight behind the liver and the full-thickness nature of the disease in all eight patients. Laparotomy with full thickness resection of the diaphragm resulted in complete eradication of symptoms in seven of eight patients, and good symptomatic reduction in one. Treatment of diaphragmatic endometriosis by laparotomy results in a high rate of symptom relief. Laparoscopic treatment of diaphragmatic endometriosis will result in a high rate of incomplete diagnosis and incomplete treatment with a high rate of continuing symptoms.