PURPOSE: To evaluate the ability of preoperative phenylephrine testing to predict postoperative upper eyelid tarsal platform show in patients undergoing Müller muscle-conjunctival resection (MMCR) ptosis repair without concurrent blepharoplasty. METHODS: A retrospective chart review was performed on 52 eyelids of patients who underwent MMCR without external skin incision. Photographs were reviewed to objectively and subjectively compare the results of phenylephrine testing to postoperative appearance. Only patients who underwent successful MMCR were included in the study. The authors defined successful MMCR as having a resulting marginal reflex distance within 1 mm of that predicted by phenylephrine testing. For objective analysis, the tarsal platform show was measured using computer software. For subjective analysis, 2 experienced examiners were asked to grade the correlation in appearance on a scale of 1-5 (1 being poor correlation and 5 being excellent correlation). RESULTS: The mean tarsal platform show in the phenylephrine test photographs and the postoperative photographs was 3.8 and 3.63 mm, respectively (mean = 0.17; standard deviation = 0.71). The difference between the means was not statistically significant (p > 0.05). The mean difference in tarsal platform show between phenylephrine testing and postoperative was 0.17 mm (standard deviation = 0.71). The difference was not statistically significant (t[51] = 0.09; p > 0.05; 2 tailed). The mean subjective correlation score comparing phenylephrine testing photographs to postoperative photographs was 4.4 out of possible 5. CONCLUSIONS: Phenylephrine testing exhibits good predictability with regard to eyelid appearance after successful MMCR without external skin incision and, therefore, may assist the surgeon when trying to decide if blepharoplasty or eyelid crease formation is necessary at the time of MMCR.