This was our 5th cruise, but the first on Celebrity. We choose Celebrity because of the itinerary and the ratings of the Company. We boarded the Century in Barcelona on Oct. 20, 2008. When we got to our cabin and started checking it out, the mildew/mold smell in our bathroom was overwhelming. We immediately called our cabin Steward and asked him to do something about it. He did try, but never really got the smell out. We even had the plumber come to flush out the drains. The second problem was diesel fumes in our cabin. The second morning I woke up with my eyes almost swollen shut and my nasal passages burning. I started taking all of my allergy medications, but progressively got worse. After returning from our excursion that day, I went to the infirmary where the Dr. gave me a nebulizer treatment and had me start an antibiotic and steroid pack. I had 2 nebulizer treatments a day during the remainder of the cruise. We had told the Dr. about the diesel fumes and mold. By about the third day, my Husband was starting to feel ill. We had spoken with someone at the Customer Service desk and told them what was going on, but all they did was write it in their book and said they would look into it and get back with us. Next to the last day of the cruise, we got a call from them asking if were still experiencing a problem. One of our table mates for dinner had smelled diesel fumes in their cabin for two days. We also heard people around the ship commenting about the diesel fumes. My Husband and I both had to go to the Dr. after we got home. I had terrible wheezing in my lungs and was sick for 6 weeks. My Husband was sick for 2 weeks. It is incomprehensible to me that the staff did not take this problem more seriously. This is a major health hazard, and they just ignored it. The third problem was our toilet. The second night out, we got back from dinner and our toilet would not flush. We called and were told that it was a system wide problem. It was not working all night, but the next morning it was finally resolved. Then the last day of the cruise was a day at sea. The toilet went out four times. This time it was only our toilet. The plumber had to come to our room each time to open the panel in the wall and work on the lines. And finally, we could smell sewer gas while walking down our hall and several other places on the ship. Maybe the problem with our toilet was more wide spread than they led us to believe. We would hold our breath while walking in certain areas because the smell was so strong. Our trip was completely ruined by this ill-maintained vessel and it's unprofessional crew. I have been in contact with Celebrity three times in writing and twice by phone since our return. The "best" they can do is to say they are sorry we did not have a good time and offer a $300 certificate toward our next cruise with them. It will be a very cold day when we get on one of their ships again.