The purpose of this study was twofold: first, to create an index for a behavioral linkage analysis of serial sex crimes, and second, to construct a predictive model for the analysis. Data on 720 sex crimes (rape, indecent assault) committed by 360 offenders arrested between 1993 and 2005 throughout Japan were collected. The following seven behaviors were examined during a series of analyses aimed at illustrating the effectiveness of crime linkage in serial sex crimes: victim age group, area type, publicness of offense site, weapon, time, contact method, and day of the week. The results indicated that six of the seven behaviors (excluding "day of the week") significantly distinguished between linked and unlinked crime pairs. Under a logistic regression of these six variables, which were dichotomously coded in terms of the concordance or discordance between each pair of incidents, the area under the receiver operating characteristic (ROC) curve was 0.85 (95% CI = 0.82-0.87), indicating a high level of discriminative accuracy in identifying disparate sex crimes committed by the same person.