Scientists think it's because the affluent patients have more opportunities for tanning.
Melanoma is a particularly deadly form of skin cancer.
Researchers studied data from Caucasian girls and women ages 15 through 39 in California.
In the richest 20 percent of California neighborhoods, four or five out of 100,000 were diagnosed with melanoma over a 5-year period.
For the poorest group, the rate was less than one in 100,000 over the same period.