Judas Iscariot is mentioned only a few times in the canonical gospels. The apostle whose name is generally rendered in English as Saint Jude was actually named Judas son of James, and outside the New Testament the apostle Saint Thomas is sometimes called Judas Thomas Didymus. Some persons have speculated that Judas Iscariot is the same as one or both of these persons, and have advanced as support for their theory the fact that some manuscripts refer to Judas son of James as Judas the Zealot, which they link with the theory that the name Iscariot refers to the Sicarii. However, the list of the Twelve in Luke 6:15,16 clearly treats Thomas, Judas son of James, and Judas Iscariot as three separate persons and the list in Acts 1 treats Thomas and Judas son of James as still alive at a time when Judas Iscariot is dead.

John 14:22 indicates that Jesus had a disciple called "Judas (not the Iscariot)," probably Judas son of James or possibly Thomas. The latter identification is less likely, since Thomas is not called Judas anywhere else in the New Testament, but it is supported by the authors of the New American Bible footnotes.

Another New Testament Judas, Jesus' brother Judas, is referred to in Matthew 13:55 and Mark 6:3. He may be the same person as Judas son of James (his different father would be explained by the Roman Catholic theory that Jesus' so-called "brothers" were really his cousins), or, in view of the statement in John 7:5 that "even his brothers did not believe" in Jesus, he may be someone else. Judas was a common name in New Testament times, and any attempt to identify the various Judases with each other should be approached with caution.