Adults adopt a vegetarian diet for various motivations, but it is unknown their overall diet quality based on a primary motivation. The purpose of the study was to compare overall diet quality, nutrient intake and related food groups based on primary motivation for following a vegetarian diet. It was hypothesized that vegetarians who chose the diet for health-related motivations would have a higher diet quality based on the Healthy Eating Index (HEI)-2015 scores compared to those following the diet for other motivations. A cross-sectional study was conducted online in the United States. Participants (n = 511) completed an 18-item questionnaire and a 24-hour recall using the Automated Self-Administered 24-hour Dietary Recall (ASA24-2018) and were divided into one of three groups (Health, Animal, Other [family, religious beliefs, or environment]) based on their primary motivation for following a vegetarian diet. Total HEI-2015 scores were determined and Kruskal-Wallis ANOVA on Ranks with a Dunn's Method for all pairwise comparisons (p < 0.05) were conducted. Results showed that total HEI-2015 scores differed among groups (p = 0.022) with the Health group having a higher score than the Other group (70.2 [57.0, 79.1] versus 63.6 [52.2, 77.1], median 25th, 75th) but not the animal rights group (66.5 [55.1, 77.0]). Higher component scores for total protein foods, seafood and plant proteins and fatty acids contributed to the significant difference. Adults who were motivated by health to follow a vegetarian diet had a higher diet quality than those who cited Other as their primary motivation. As motivations may impact diet quality of vegetarians, it is necessary to account for them.