Complications from circumcision are much more common that most parents realize.

Bleeding

Excessive bleeding is the most common immediate complication associated with circumcision.  Abnormal or excessive bleeding occurs in ~10% of circumcisions.

Infection

Infection is the second most common early complication of circumcision.  Infection occurs in approximately 8% of cases, and can progress to systemic infection, partial or complete loss of the penis due to necrosis, or death.

Pain

Research confirms that babies have the capacity to feel and remember pain.  Pain is an inevitable consequence of circumcision, regardless of whether anesthesia is used.  A Cochrane Review of 35 clinical trials concluded that dorsal penile nerve blocks and topical lidocaine-prilocaine do not eliminate circumcision pain.  Pain from circumcision has been demonstrated to cause permanent physiological and psychological changes, including upregulation of cortisol, site-specific changes in the brain that are associated with mood disorders, PTSD, an increase in depressive symptoms and anxiety, lower regulation of emotions, and increased incidence of anger.  The pain of circumcision has been repeatedly shown to interfere with successful breastfeeding.  A study in Denmark demonstrated that the risk of autism doubled among boys who had been circumcised.

Surgical Complications

A common complication is the removal of too much skin, which can cause partial or total denudation of the penile shaft.  Removal of too much skin can also result in painful erections or scrotal skin being pulled onto the shaft.  The urethra can be damaged, resulting in pressure necrosis or urethral fistulas.  In approximately 1% of cases, the glans or entire penis may be amputated or lost to necrosis.

Delayed Complications

Meatitis and meatal stenosis (narrowing of the urethral opening) occurs in ~1% of cases.  Adhesions and skin bridges in approximately 25% of circumcised boys.  Phimosis (tightening of the remaining foreskin behind the glans) occurs in approximately 2% of boys, over three times the rate of phimosis in uncircumcised boys (one of the common surgical justifications for circumcision).  Approximately 5% of boys will require additional surgery to correct problems caused by a previous circumcision.

Death

Current mortality rates from circumcision are approximately 1 in 11,000.