Background. Although more than 100 million passengers have taken a cruise since 1980, it is not known what dental treatment needs occur at sea. Methods. The routine dental documentation of a 2-month period at sea on a cruise ship carrying 1,619 passengers was analyzed. The subjects for the study were 57 passengers (3.5% of 1,619), with a mean age of 71 years (±9.8 y). Age, gender, number of natural teeth and implants, prosthetic status, diagnosis, treatment performed, percentage of emergency and routine procedures, number of appointments, duration of appointment, time since last visit to the dentist, and cabin category as indicator of socioeconomic status were extracted. Oral health-related quality of life (OHRQoL) was measured using the 14-item Oral Health Impact Profile. Results. Passengers had a mean number of 20 natural teeth plus substantial fixed and removable prosthodontics. Emergency dental treatment accounted for 97% of the chairside time. The three most frequent emergency diagnoses were defective restorations (36%), pulpal disease (20%), and defective prosthesis and caries (both 11.5%). Common emergency therapies provided were complex surgical-prosthodontic rehabilitation, various endodontic treatments, and extractions. Per 1,000 persons/month, passengers required 21.6 emergency plus 2.5 routine appointments; 49% of passengers had seen a dentist within 3 months before going to sea. Conclusions. Passengers do attend their dentist for routine care/checkups before the voyage, yet experience complex dental emergencies. This is due to the presence of a high number of restorations that fail unexpectedly. Some failures are so severe that they would have forced the passenger to abort the cruise had there been no dental service available. The ease of access to quality dental care may explain the relatively low level of perceived problems as characterized by OHRQoL scores.