As part of a doctoral study, the critical thinking dispositions of post-RN (post-diploma) nurses continuing their education at a mid-sized university were measured before and after the intervention of a three-credit online course. The tool used to measure the changes in critical thinking disposition was the California Critical Thinking Dispositions Inventory (CCTDI). There were no statistically significant increases in the participants' overall measures of critical thinking dispositions as a function of online study. A time interaction effect suggested that students generally show gains in a critical thinking disposition called truthseeking as a function of university experience. (Contains 6 tables and 2 figures.)