This article offers a new reading of the well-known diary kept by the Florentine apothecary Luca Landucci between 1450 and 1516, examining its accounts of prodigies and other "monstrous" occurrences from a modern scientific point of view. Particular consideration is given to descriptions of a variety of birth defects observed in various Italian cities at the time, providing explanations for each case based on the latest medical theories. A detailed analysis is provided for a case of cranioschisis recorded in Volterra in 1474, a case of Opitz syndrome occurring in Venice in 1489, the birth of conjoined twins in Padua in the same year, conjoined triplets born to a 60-year-old woman in Venice, the well-publicized account of the 1512 Ravenna monster and, finally, the thoraco-acephalus tetramelus adolescent that Landucci personally observed in Florence in 1513.