Endometriosis CAN cause infertility.
More Info: Ten percent of all infertility cases are caused by endometriosis making it one of the top three causes of infertility. (Ovulatory disorders are indicated in 30% of the cases, tubal disease in 25%, the remainder is unidentified). Endometriosis affects more than 176 million women worldwide. 
How Does Endometriosis Affects Fertility?
Endometriosis is a condition in which the cells from the lining of the uterus grow in other areas of the body such as the ovaries, bladder, and bowels. Unlike the healthy cells of the lining of the uterus that shed during menstruation, those outside of the uterus do not. These endometrial tissue implants can cause infertility if they block the egg from traveling its natural course from the ovaries through the fallopian tubes.
Research is also beginning to suggest that endometriosis may cause a luteal phase defect. It is during this phase that the uterine lining grows thicker in preparation for a fertilized egg to implant. This makes it difficult to become pregnant with some studies suggesting that endometriosis is the cause of 36% of spontaneous abortions. 
Does Endometriosis Always Cause Infertility?
It is estimated that forty percent of the women with endometriosis will experience fertility issues to some degree.  Several factors apply the most critical being the severity of the condition as well as where the endometrial tissue implants are located. Those with mild to moderate endometriosis may not have any trouble conceiving. Even those with infertility issues due to the condition may have the option for laparoscopic surgery to remove scar tissue that is interfering with the ability to get pregnant.
How Infertility Caused by Endometriosis Is Diagnosed
Laparoscopy: The first step in detecting whether or not endometriosis is the cause of infertility is to accurately diagnosis that endometriosis is present. Laparoscopy involves a small incision beneath the navel through which a viewing device is inserted. A physician can then view the fallopian tubes, uterus, and ovaries. The procedure is usually done on an outpatient basis under general anesthesia. Though there are other methods that can point to endometriosis, a laparoscopy is currently the most accurate. 
Hysterosalpingogram: A dye is injected into the uterus, which will travel through the fallopian tubes. X-rays will indicate any problems such as blockage. 
Ruling out Other Causes: Having endometriosis does not always mean it will cause fertility issues. Tests can be performed to check for additional causes such as hormone testing, ovulation testing, genetic testing, and ovarian reserve testing. 
 Endometriosis Foundation of America
Endometriosis Facts and Statistics
 National Infertility Association
How Is Endometriosis Diagnosed?
 Mayo Clinic
Infertility-Tests and Diagnosis
Resource: Stanford University
What Causes Female Infertility? http://www.stanford.edu/class/siw198q/websites/reprotech/New%20Ways%20of%20Making%20Babies/Causefem.htm
Resource: National Center for Biotechnology Information
Glossary of Terms
Genetic Testing: tests on blood and other tissue to find genetic disorders. About 900 such tests are available.
Luteal Phase Defect: a disruption in a woman’s monthly menstrual cycle. The luteal phase is one stage of the menstrual cycle. It occurs after ovulation (when the ovaries release an egg) and before your period starts.
Ovarian Reserve Testing: one mechanism by which fertility specialists can partially predict the reproductive potential of a specific patient as well as the potential of her eggs to result in a healthy pregnancy.
Ovulation Testing: A blood test is sometimes performed to measure hormone levels to determine whether you are ovulating.
“Whether or not so-called “mild” endometriosis affects fertility has remained controversial. At CHR, we strongly believe that endometriosis, even when mild, can negatively affect fertility. Even more importantly, endometriosis affects fertility adversely in many different ways, though its effects on normal tubal function appear to be the most important.”
Endometriosis Fertility and Treatment Options Center for Human Reproduction-New York