Chalfin H, et al. - Given a wide use of RENAL nephrometry score (RNS) to define renal mass complexity and inform patient counseling for partial nephrectomy (PN), but it is not known which features drive postoperative complications in cases with multiple lesions (often noted in hereditary cancer syndromes), so, researchers used a new scoring equation (Multiplex Score, MS) derived from RNS and evaluated results of multiplex PN at their institution. A single surgeon performed a total of 62 consecutive multiplex PN (median (range) # tumors = 4 (2-11), 65% robotic) from 10/2017-8/2019. Median (range) MS was 6 (2-20). Every 1 additional high risk or intermediate risk tumor was found to be related to a 2 minute increment in clamp time. Overall, a good correlation of the new Multiplex Score with complications, blood loss, and open conversion was shown. Standardized reporting of complexity for multiplex series may be facilitated by this instrument, with particular significance for hereditary cancer syndromes.