R. Lampronti's main reputation, however, rests on his monumental Pahad Yizhak, two editions of which he wrote himself, the first consisting of 120 and the second of 35 manuscript volumes. Pahad Yizhak is the most comprehensive and well-known encyclopedia in the field of halakhah. It is arranged alphabetically, each article including material from the Mishnah, the Talmud, the posekim, the rishonim, and the responsa literature. He pays special importance to the responsa literature of Italian rabbis, some of which was otherwise unknown, and quotes from it extensively. Many of his own responsa, which are not included in the Pahad Yizhak, appear in the responsa collections of his contemporaries, such as the Shemesh Zedakah (Venice, 1743) of R. Samson Morpurgo. On the other hand, his many sermons have been lost. The first portion of the Pahad Yizhak (letters alef to mem) was published in Italy between 1750 and 1840, and the remainder in Germany between 1864 and 1887. Of the second edition, only two volumes appeared, containing the letters alef to het (1935–42). The publication of both editions together has been undertaken in recent years (letters alef-alef to alef-shin appeared, 1962–66).

חלק ד: אותיות י כ ל. ויניציאה, חש"מ - ריגייו, דפוס חנניה אלחנן חי כהן, תקע"ג. [1], קח; כח דף.