The Confraternity of Saint Jerome in Udine (Confraternita di San Girolamo degli Schiavoni) was founded in 1452 by secession of members of Slavic origin who, during the first half of the 15th century, formed a part of the Confraternity of Germans (Confraternita della Santissima Trinità). Their first seat was located at Borgo Sant’Antonio and they congregated around an altar dedicated to St Anthony Abbot in the Dominican church of St Peter the Martyr. In 1482 they took over an altar dedicated to their patron St Jerome, in Udine Cathedral and moved their seat to the more prestigious location in its vicinity. The edifice was enlarged in late 15th century. It was successively rebuild in 16th and 18th century, but unfortunately largely demolished in 1935. The Confraternity itself was abolished by the civil government in 1775. The research will examine the patronage activities of the Confraternity including the history of former seat as well as recorded furnishings of its altar in the Cathedral, with particular attention to the most prominent work of art connected to the Confraternity, an illuminated manuscript containing its rules from 1479, kept in Udine City library (Biblioteca civica).