OBJECTIVE Monopolar radiofrequency skin heating coupled with cryogen cooling of facial skin for skin tightening has been utilized on over 10,000 patients since 2002. In order to establish the actual rate and degree of side effects in our clinical experience, a retrospective chart review was performed. METHODS Charts and clinical images of over 600 consecutive patient treatments between May 2002 and June 2006 using a monopolar radiofrequency device (Thermacool, Thermage, Haywood, CA) for skin tightening at the Maryland Laser, Skin and Vein Institute were retrospectively reviewed. The primary presentation for treatment was skin laxity of the lower face. Treatment was delivered with a 1-cm2 standard tip at fluences of 81 to 124 J/cm2 (level of 12.5 to 15), a 1-cm2 "fast" tip at fluences of 62 to 109 J/cm2 (level of 72.0 to 76.0), a 1.5-cm2 "big fast" tip at fluences of 75 to 130 J/cm2 (level of 61.5 to 65), and a 3-cm2 "bigger" tip at equivalent fluences as each became available. As treatment algorithms evolved over 4 years, the algorithm of multiple passes at lower fluence associated with better clinical outcomes and greater patient acceptance has been adopted. RESULTS The most common immediate and expected clinical effects were erythema and edema lasting less than 24 hours, although 6 patients reported edema lasting for up to 1 week. There were no permanent side effects. In total, 2.7% of treatments resulted in temporary side effects, the most significant of which was a slight depression on the cheek (n = 1), which completely resolved within 3.5 months. Other side effects included localized areas of acneiform subcutaneous erythematous papules (n = 4) and a linear superficial crust (n = 1) with the original tip, all of which resolved within 1 week. One patient reported small erythematous subcutaneous nodules resolving in 17 days. Tenderness of the neck lasting from 2 weeks (n = 2) to 3 weeks (n = 1) was also reported. CONCLUSIONS Our data, obtained in an office setting without injectable anesthetic or i.v. sedation, indicate that monopolar RF for skin tightening is a very safe procedure. The treatment algorithm and tips have evolved over several years leading to increased safety and efficacy. Side effects are infrequent, self-limited, and minor, comparing favorably to other nonablative devices utilized for facial rejuvenation.