First he had a 'bodily ailment' which he recognized as a trial to his converts and prayed for deliverance. Galatians 4:13-15; 2 Corinthians 12:7-10
Secondly there was the 'marks of Jesus' left on his body which were probably the marks of physical abuse suffered as a minister of the Gospel. 'Sacred Brands' Galatians 6:17
He also recognized that he wasn't the greatest preacher. 1 Corinthians 2:1-5; 2 Corinthians 10:10; 11:6 However this does not mean that Paul was not an wise and intelligent servant of God. He displayed a strong character and infectious spirit in the ministry.
A Bishop in the province of Asia during the second century described him as 'a man small of stature, with a bald head and crooked legs, in a good state of body, with eyebrows meeting and nose somewhat hooked, full of friendliness: for now he appears like man and now he had the face of an angel '(Acts of Paul and Thessal 3).
from:
http://www.abu.nb.ca/ecm/topics/people15.htm