Objective: Transillumination and laparoscopic visualization are two techniques recommended to minimize the risks of injury to abdominal wall structures during insertion of secondary trocars. This study was designed to determine the effectiveness of these techniques to locate the epigastric vessels and superior bladder margin. Design: Prospective observational. Setting: Academic medical centers. Patient(s): One hundred five women undergoing laparoscopy for tubal sterilization, infertility, pelvic masses, or pelvic pain. Intervention(s): None. Main Outcome Measure(s): The ability to visualize the superficial and inferior epigastric vessels, and bladder margin; body mass index (BMI; in kilograms per meter squared); and skin color. Result(s): Transillumination successfully visualized 64% of superficial epigastric vessels and was less effective both as weight increased (BMI <25 kg/m2: 86%; BMI = 25-30 kg/m2: 61%; BMI >30 kg/m2: 25%) and in dark-skinned women (69%) compared to those with lighter skin (42%). Laparoscopic visualization successfully identified 82% of inferior epigastric vessels and 46% of bladder margins, and was less effective as weight increased. Conclusion(s): Transillumination can successfully locate superficial epigastric vessels, and laparoscopic visualization can locate inferior epigastric vessels and the superior bladder margin in the majority of women undergoing laparoscopy. Transillumination is less effective in dark-skinned women, and both techniques are less effective with increasing body weight. © 2003 by American Society for Reproductive Medicine.