In 179 consecutive laparoscopies for infertility (n = 105), pain (n = 60), or both problems (n = 14), endometriosis was diagnosed in 77%, 82%, and 86%, respectively. Eighty implants with positive histology and with careful assessment of depth were sampled by CO2 laser excision from 53 patients. Deep (greater than or equal to 5 mm), intermediate (2 to 4 mm), and superficial (less than 1 mm) infiltration was found in 48%, 35%, and 17% of implants, respectively. Deep infiltration was observed in the pouch of Douglas (55%) and at the uterosacrals (34%), but was absent from the ovarian fossas. Deep implants were found to be active in 68%. At an intermediate depth, however, only 25% of implants were active, whereas 58% of superficial foci showed activity. Deep implants were in phase with the endometrium in 74%. At an intermediate depth, however, only 38% showed regular cyclicity, whereas 57% of superficial implants were in phase with the cycle. Deep infiltration occurred through loose connective tissue septa into the fibromuscular tissue and was always stopped at the underlying fat tissue. Very deep implants (greater than 10 mm) were found exclusively in patients with pain; superficial implants, on the contrary, were found most frequently in patients with infertility (83%).