What is premillenialism?  It's the teaching that when Christ comes again He will set up an earthly kingdom and reign with His saints for a thousand (millenium) years before (pre-) taking the kingdom up to heaven  There are a variety of variations to this basic theme which should be a signal that this is not solid teaching from the Scriptures.  It's interesting to note that many cults discounted this doctrine (which also includes the doctrine of the Rapture) well over fifty years ago and only in recent times has it been revived.  The main verse by premillenialists to support their belief is Revelation 20:4 and the verse used to support the Rapture is 1 Thessalonians 4: 15-17.

1)  OBVIOUS CONFLICTS
     a.  Taken literally, the Revelation 20:4 would mean that the only ones who are going to be a part of this thousand year reign are those who have been beheaded for the word, those who did not worship Rome (the beast) and those who did not reeive the mark on their forehead.  None of us fall into any of those categories.
    b.   If you are to believe premillenialism and the Rapture together, then 1 Thessalonians would conflict with Revelation in that one would have Jesus remaining in the air and the other having Him come to the earth.  The scripture does teach that the redeemed will meet the Lord but not in the sense of a reign as proposed in premillenial doctrine.
   c.  There are many aspects of the Rapture that are foreign to Scripture.
        1.  "silent" in nature
        2.  number of resurrections
        3.  etc...

2)  WHEN THE KINGDOM WOULD BE ESTABLISHED
     a.  Premillenial theory has the Lord coming back to set up His kingdom sometime on the future, but Christ is King of kings now. (1 Timothy 6: 15)
     b.  A king with no kingdom is no king at all.
     c.  In Scripture with the beginning of the Church in Acts 2 the Kingdom is always spoken of in the existing sense.
     d.  The following verses verify this..
          1.  Colossians 1:13- Kingdom of His dear Son" - Revelation 1:9 - Kingdom in Christ Jesus  -1 Corinthians 15: 23-24- delivers up the Kingdom (now in existence)
     e.  One more Scripture for your consideration will show when the kingdom was to come 
          1.  Mark 9:1 - In the gospels Jesus tells His audience that some of them will not die until they see the kingdom of God come.

3)  TIME LIMITATION TO SCRIPTURES
     a.  Many passages used for the Second Coming of Christ and a thousand year reign on earth are drawn from either the Old Testament or the book of Revelation.  However, we never have OT Scriptures that prophesy beyond NT events.  Revelation is specific about its own time frame.
          1.  look at some of these scriptures
               a.  Acts 3: 22-24; Luke 24:47; Revelation 1:1; Revelaton 1:3; Revelation 22:10

4)   ERRONEOUS USE OF SCRIPTURE
     a.  Many "proof" passages for premillenialism and the Rapture are half passages.  Many times something is read into the context that's not there.  Books have been written about the Revelation showing the Russians would overtake Israel,  but not mentioned in the books that the scripture says bow and arrowa would be used.  Daniel 2: 36-45 refers to the four kingdoms, with the Kingdom of God coming during the Roman, or fourth.  Many today say the other kingdoms are the ten toes, but it's actually the toes are part of the fourth kingdom. (2:41).  Premillenialists also read into Revelation 20: 3-5 things that aren't there. 

Simply put, premillenial doctrine is not scriptural.