I saw mention of a ritalin cancer link in a newspaper editorial. I did a little research on the web and it seems in 1995 there was a study that found a weak link between ritalin and cancer in rats.

Here's a summary:

The study in rats revealed no cancer-causing activity. The findings in mice included increased rates of noncancerous liver tumors and, in males only, the occurrence of cancerous liver tumors.

Just curious, but I haven't heard of any actual cases in children. Has anyone else heard of real cases?