Here is a summary of what is required of a person contemplating surgery:

-- Obtain a written psychological evaluation by a licensed psychologist or psychiatrist with training in sex therapy. Patient-applicants must have a confirmed diagnosis of gender dysphoria and have completed at least three months of psychotherapy before beginning hormone therapy.

-- Take the hormone-therapy evaluation to an endocrinologist who will explain what the patient may expect from the hormones, both positive and negative, and regularly monitor the patient's lab work.

-- While continuing hormone therapy, the patient must live for two to three years in the gender of orientation. The patient must demonstrate stability, become self-supporting and be socially active. This process usually begins after the patient has been on hormones long enough to move freely in the opposite gender. Other nongenital surgeries and electrolysis are generally performed by this time.

-- After at least one year of cross-living, the patient receives the final psychological evaluation before surgery.

The fees vary, depending on how extensive the surgery and where it is performed. In the United States, male-to-female surgery costs $10,000 to $45,000; female-to-male, $25,000 to $100,000.

The surgery is painful and irreversible. For a male-to-female transsexual, surgeons amputate the penis, remove the testes and reroute the urethra, then turn the penis inside-out to build a vagina. For the next six weeks, the patient must keep a condom filled with foam rubber inside the neovagina to keep it open. A rigid vaginal dilator is inserted at least once a day.

Female-to-male surgery is even more extensive. Generally, the patient undergoes several operations including a mastectomy, full hysterectomy, closure of the vagina, and construction of a neopenis and scrotum that will house artificial testes. The neopenis is usually nonfunctional for urination and can become erect only by inserting stiff material or via a system of inflatable plastic tubing inserted in the groin. Sometimes, patients forgo phalloplasty in favor of a hormonally enlarged clitoris.

Not everyone who seeks sexual reassignment gets approval; in fact, many are rejected. ``The significant part of successful transsexual surgery is not the operative technique itself,'' writes Larry I. Lipshultz, a professor of urology at Baylor College of Medicine in Houston. ``More important is the method of careful and correct patient selection.''

Nor does every transsexual seek surgery. Increasing numbers of people who in the past might have sought surgery now are satisfied to accept themselves in a gender-blended state.