Study published in the Journal of Urology, Volume 167, Issue 5, Pages 2113-2116 (May 2002).  The study's purpose was to determine the effect of the prepuce (foreskin) on sexual intercourse. The researchers examined sexual function outcomes in men who experienced sexual intercourse in the uncircumcised and circumcised states.

The study chose as subjects men who were circumcised for medical reasons. Only 7% of the men were circumcised as elective surgery. Even with such a large proportion of the subjects being circumcised for having problems with their foreskin, 38% reported that it was worse being circumcised.

Study published in BJUI (British Journal of Urology International), Volume 99, Issue 4, Pages 864-869 (March 2007). This is the Sorrells study. The Sorrels study is remarkable because it used objective measurements to determine fine-touch sensitivity of various parts of the intact penis and the circumcumcised penis, showing that circumcision removes the most sensitive parts of the penis.

Watch a YouTube video of Dr. Sorrells discussing the study and his results.

A study published in Urologia Internationalis, Vol. 75, No. 1, 2005 (Urol Int 2005;75:62-66) (DOI: 10.1159/000085930). The authors assessed the effect of circumcision on sexually active men and the relative impact this may have on informed consent prior to surgery. 

The male subjects were circumcised for a benign desease. Penile sensation got worse for 18% of the men who got an adult circumcision. Only 61% of the men were satisfied with their adult circumcision. Considering that circumcision was for a disease, it is significant that not more men were satisfied with the cure.

Study published in British Journal of Urology (BJU Int.) 2009 Apr; 103(8):1096-103. Epub 2009 Feb 24. The study used a self-reported questionaire and reports on various genital and nongenital areas in terms of erotic sensitivity for intact men (uncircumcised).

A documentary type video with information on several men's experiences with their intact foreskin regarding sensitivty. A circumcised man asks questions and provides his impressions.  The video provides a wide perspective of the variations of sensitivity and foreskin length. The video is embedded here or go to YouTube to see it.

Dr. Morris L. Sorrells M.D. discusses the penile sensitivity tests he and other doctors conducted that studied circumcised and intact penises. They concluded that circumcision ablates the most sensitive parts of the penis. That is, circumcision removes the best part of a man's sex organ. Read about his study: Fine-touch pressure thresholds in the adult penis. See the video below: