Although the development of collaborative relationships is considered a requirement for medical education, the functioning of these relationships may be impaired by a well-documented social-psychological phenomenon known as group conformity. The authors hypothesized that students would insert a needle into an incorrect location relative to the patella when performing a knee arthrocentesis if they believed that their peers had also inserted a needle in the same incorrect location. This was a randomized controlled study conducted in 2011 with 60 medical students (24 male; 40.0%) who were randomly assigned to either using a knee model that had a skin with holes left by peers inserting needles in the wrong location, or a knee with no marks in the skin. Each student's aspiration site was measured with a fibreglass ruler to determine whether it was correctly located within the superior third, 1 cm medial to the patella. The researchers determined that students who used the marked skin were more likely to insert the needle in the incorrect location compared to those who used the clean skin (n = 31, 86.11 vs. n = 14, 58.33%), Fisher's exact test (1) = 5.93, p < 0.05, Cramer's ? = 0.31. This study demonstrates incorrect performance of the knee arthrocentesis procedure in simulation when students use a damaged model, which may be due to conformity. It suggests that further research on the impact of conformity in medical education is warranted.