We went to Breck in January and again in april... a couple in our party experienced altitude sickness. the 2nd time we went, I went prepared. I purchased cans of oxygen and brought them with me. although my son still had some headaches, but he didn't throw up like last time because I made sure the first couple days we were there he drank lots of water and breathed in extra oxygen through out the day and had electrolytes, not usually one to have them drink Gatorade, but that also seemed to help too. it made a huge difference and we were able to enjoy the mountain the first day we were there rather than taking so long to acclimate. Also, for anyone that is bringing first time skiers to keystone or breck, and don't want to spend the outrageous prices on lessons, check out ski lessons at the frisco adventure park. our kids did a 2.5 hour ski lesson there and they were able to hit the slopes the following day and going down blues the day after.