I'm 42, healthy, n/s. random ct in march showed several tiny lung nodules. no change in sept ct except 1 grew from 5mm to 6mm. i'm afraid it's cancer?

Probably not.: From march to sept (6 months), it only 'grew' 1 mm. This, given the limitations of ct, would not be considered true growth and is very unlikely to be lung cancer, especially because you are young (42) and a non-smoker. Do, however, follow your physician's advice about reimaging and follow-up.

Observation: Most nodules seen on ct scan are benign (95%). The size make them too small to biopsy, and the change in size could be due to study variation. You should talk to your physician and have the study repeated in three months. If there is no change, relax. If the one nodule is bigger, biopsy or resection would be appropriate.