Background: The UVB-vitamin D-breast cancer (BC) hypothesis is supported by ecological studies demonstrating an inverse correlation between sunlight exposure and BC incidence and mortality. Observational studies also favor an inverse association between vitamin D status and BC risk, recurrence and mortality. Yet controversies remain regarding the role of vitamin D in BC. We examined associations between vitamin D levels, geographic location, clinical, and pathologic characteristics of BC patients (pts). Methods: This was a retrospective analysis from the electronic health record database of pts diagnosed with BC between 1/2007 and 5/2013 across US Oncology Network practices categorized based on their geographic location into: northern (> 40° N), central (35 to 40°N) and southern (< 35°N) latitude. We collected age at diagnosis, BMI, smoking history, stage, estrogen receptor (ER), progesterone receptor (PR), HER2 status, and the first documented serum 25-hydroxyvitamin D (25-(OH)D) level, categorized as 30 optimal. Statistical comparison was performed using Chi-squared tests for categorical variables and Kruskal-Wallis tests for continuous variables. Logistic regression was used to predict the likelihood of vitamin D deficiency. Results: 20,338 BC pts with a documented vitamin D level were identified. Mean age at diagnosis was 58. Stage and receptor status distribution were: 8%, 41%, 32%, 11% and 4% for stage 0, I, II,III, and IV respectively; 63%, 13%, and 10% for ER+/HER-2-, HER-2+ and TNBC, respectively. 17.6% and 27.8% of pts had deficient or suboptimal vitamin D levels. The covariates of age < 60 years (OR 1.24), advanced stage (OR 1.32 stage II, OR 1.51 stage III, and OR 1.81 stage IV), TNBC (OR 1.45), BMI ≥ 25 (OR 2.02), current smoker (OR 2.11), and lower latitudes (OR 1.36 and 1.19 for central and southern latitude respectively) were independent predictors of a first documented vitamin D deficiency in a multivariate model. Conclusions: Vitamin D deficiency may be associated with TNBC and central and southern latitudes. The possible influences of differential vitamin D supplementation and timing of testing require further investigation.