Actually there are now more cases of malaria in the U.S. than in Belize (of course Belize has a much smaller population). The risk of malaria in Belize has fallen dramatically over the past decade or so. At one time in the early 90s there were some 8,000 cases a year, now fewer than 1,000 in the entire country, mostly among immigrant groups in border areas especially southern Belize.
The Centers for Disease Control, which is very conservative in its recommendations, notes there is risk of malaria in all areas of Belize except Belize City. Chloroquine, a long-used drug with few if any side effects (I took it years ago in the army in Vietnam) is the recommended prophylaxsis if any is taken.
But as a practical matter the risk on Ambergris Caye is very, very, very slight -- probably about the same as going to Florida or Louisiana.
Better safe than sorry I guess but the vast majority of visitors to San Pedro and to other other cayes do not take chloroquine and certainly the residents don't.
Belize books and publications by Lan Sluder:
Belize First Magazine (http://www.belizefirst.com
Fodor's Belize & Guatemala Guide (new 4th edition coming this fall)
Adapter Kit: Belize (the first and only comprehensive guide to living, retiring, working and investing in Belize -- a best-seller on Amazon.com)
San Pedro Cool (the first and only visitor guide to Ambergris Caye)
Belize First Guide to Mainland Belize -- sold out, new edition coming early 2003
UpClose Central America
Belize Book of Lists -- sold out, new edition coming early 2003
Best Hotels of Belize -- coming late 2002