This study determined urinary creatinine levels and their relationship with dietary habits of subjects. The female subjects (20) filled out a survey with basic demographic and anthropometric data, and a three-day food diary. Vegans had no dietary intake of creatine, and it was 0.49 ± 0.22 g/day in omnivores. Mean urinary creatinine level in the vegan group was 0.8 mg/mL, and 1.1 mg/mL in the omnivore group, respectively, but this difference was not statistically significant. Vegans had a greater intake of dietary fiber, Fe, and Cu, while omnivores consumed more total protein and fat, saturated and monounsaturated fat, Ca, P, and vitamins B2, B12, and D. Statistically significant positive correlation was determined between Ca intake and urinary creatinine levels (R = 0.46, p = 0.039), and correlations with energy, cholesterol, vitamins B12, and D intakes were near the margin of significance. Vitamin B12 was the only nutrient that was significantly correlated with urinary creatinine in vegans (R = 0.64, p = 0.044). No statistically significant relationship was established in the omnivore group. Considering the large differences in intake and small differences in urinary creatinine concentrations, it is obvious that an increased endogenous biosynthesis of creatine compensates for an inadequate dietary intake in vegans. Intake of meat by omnivores and intake of nutrients that stimulate creatine biosynthesis by vegans are the probable reasons for the positive correlations between selected nutrients and urinary creatinine levels.