OBJECTIVES: A high proportion of patients consume pharmacological resources during a hospital admission  but  little is known about the characteristics of those not receiving a drug prescription (DP).The aim was to assess independent patient’s factors related to a non-DP  during admission. METHODS: Retrospective observational study including all patients admitted in a teaching hospital during 2010. Exclusion criteria:  direct admission at the Intensive Care Unit. Data collected: patients with and without a DP , demographics, programmed or urgent admission, Charlson score, length of hospital stay (LOS), type of Drug Related Group (DRG) (medical  or surgical), DRG weight, readmission, mortality. Statistical analysis: Univariate analysis were performed, using Chi-Square test, Fisher exact Test and Mann-Whitney U test.  A binary logistic regression was applied to identify independent factors and the model was assessed  with the area under the receiver operating characteristics (ROC) curve (AUC).  RESULTS: Patients: 16,485. Included: 15,750. Without a DP: 1,822  (11,6%) . Univariate:  Patients with and without a DP; Age: 55,40 (+24,26) vs 23,70 (+ 29,8)(p<0.001); Male: 6830(49.0%) vs 972(53.3%)(p<0.001). Urgent admission: 5,183(37.2%) vs 1,334(73.2%)(p<0.001); Charlson (0): 7,724(51.1%) vs 1,522(83.5%)(P<0.001). LOS: 8.18 (+10.00) vs 1.67(+1.63)(p<0.001), medical DRG : 8,743 (62.8%) vs 1,529(83.9%)(p<0.001); DRG weight : 1.79(+1.70) vs 0.84 (+1.55)(p<0.001); Readmission: 3.786(27.2%) vs 194(10.6%)(p<0.001); mortality: 383(2.7%) vs 47(2.6%)(p=0.675). Independent factors related to non-DP: age < 18 years (OR: 8.338, CI95%: 7.123-9.760, p<0.001), Urgent admission: (OR: 4.830, CI95%: 4.172-5.592, p<0.001), Charlson 0: (OR: 1.625, CI95%: 1.372-1.925, p<0.001), LOS < 2 days (OR: 13.711, CI95%: 11.701-16.066, p<0.001), medical DRG: (OR: 2.772, CI95%: 2.354-3.264, p<0.001). AUC: 0.917 (CI95%: 0.910-0.924, p<0.001). CONCLUSIONS: Paediatric population, an urgent admission, a low comorbidity status, a short LOS and a medical DRG were independent factors related to a non-DP during hospital admission. These patients could be managed in an ambulatory setting, what would help to reduce the economic burden in hospitals.