This article validates the theoretical effectiveness of a simple approach to identify the fertile window of the menstrual cycle. The TwoDay method identifies all days in the cycle in which the woman notices cervical secretions, and the days immediately following these days, as the period in which the woman should consider herself fertile. Women who use this method are counseled to avoid unprotected intercourse on these days. The theoretical effectiveness of the TwoDay method was tested previously by applying the method rules to the menstrual cycles of women from a large data set from the World Health Organization (WHO). For the current study, we administered the same analysis to a data set from an Italian Ovulation Method center. These data are better suited for the analysis than were the WHO data because they identify all days with secretions. Results suggest that the method can be highly effective in helping women to identify correctly the days on which they should avoid unprotected intercourse if they do not wish to become pregnant, although some users may identify a few days as fertile that actually are not.