That's a question that we should never have to ask, but unfortunately, many younger Catholics in the United States, Canada, and Great Britain are in the uncomfortable position now of having to question the validity of their own baptisms.
On Friday, February 29, 2008, the Vatican Information Service reported that the Congregation for the Doctrine of the Faith, the Vatican office chiefly responsible for ruling on doctrinal questions, had issued a response to "two questions concerning the validity of Baptism conferred with certain non-standard formulae":
The first question is: "Is a Baptism valid if conferred with the words 'I baptise you in the name of the Creator, and of the Redeemer, and of the Sanctifier', or 'I baptise you in the name of the Creator, and of the Liberator, and of the Sustainer'"?
The second question is: "Must people baptised with those formulae be baptised 'in forma absoluta'?"The responses are: "To the first question, negative; to the second question, affirmative".
Primarily during the 1980's and 1990's, but extending back into the 1960's and forward to today, some priests, mostly in English-speaking countries, abandoned the traditional form of the Sacrament of Baptism: "I baptize you in the name of the Father, and of the Son, and of the Holy Spirit." The change was a misguided attempt to avoid "sexist language."
The CDF's ruling means that any person who was baptized using any formula other than "in the name of the Father, and of the Son, and of the Holy Spirit" has not, in fact, received the Sacrament of Baptism. Christ Himself gave us this formula, and no man has the power to change it. This is very important, because Baptism is both the mark of our salvation and the "door of the Church"--the gateway to the entire Christian life. An unbaptized person cannot validly receive any of the other sacraments, including Holy Communion, Matrimony, and Holy Orders.
What should you do if you suspect that you may have been baptized using an invalid formula? The first thing you should do is to discuss this with your current parish priest. If it can be determined that you were not validly baptized, he can baptize you. If there is doubt about whether you were validly baptized, you cannot be "rebaptized" (because the sacrament can only be validly received once), but you can receive a "conditional baptism," which acknowledges the possibility that your original baptism was valid but acts as an "insurance policy" in case it was not.
If you were not validly baptized but have been married, your priest can also help you get your marriage normalized.