People dress up on all the Halloween cruises....not just the ones around actual Halloween. Our cruise where I was Cruella above was on the October 7th cruise out of NYC. I would say 90% of the guest dressed up on the Trick or Treat day!We sailed the week of Halloween and dressed up 4 nights:
Formal night - with matching nice clothes (but not a true costume)
Informal night - 1920s Gatsby themed
Halloween - 1960s Hippies
Pirate Night - Pirates
Not sure if it just happens the actual week of Halloween - but there were tons of adults in costumes throughout the week.