BACKGROUND To study the role of urinary trypsinogen-2 in diagnosing and early prognosis of patients with acute pancreatitis (AP) and the relationship to length of hospital stay and mortality. METHODS Forty-two patients were included in the study. In all cases, blood cell count, serum chemistry, urine amylase and urine trypsinogen-2 were measured. A cut-off of 50 microg/L was established and, when positive, a second dilution was made (2000 microg/L). Other variables included were etiology, mean length of hospital stay, transfer to an ICU and death. RESULTS Out of the 42 patients, 29 (69%) were men and 13 (31%) women. Average age was 61 years. The most frequent cause was biliary, followed by alcohol. Mean hospital stay was 8.38 days. Transferred to an ICU: 4 (9.5%) patients. Two of them and a third, who had not been transferred, died (7.14%). High serum amylase was found in 33 (78.57%) patients and high lipase in 36 (85.71%). Urinary trypsinogen-2 was positive in 34 patients (80.95%). Statistical association between urinary trypsinogen-2 and age (p=0.016; r=0.893), glucose (p=0.005; r=0.901), serum amylase (p=0.029; r=0.852), lipase (p=0.022; r=0.809) and hypoxemia (p=0.001; r=0.962) was found. Regarding hospital stay, there was statistical association with age (p=0.046; r=0.784) and metabolic acidosis (p=0.016; r=0.839). With respect to mortality there was statistical association with hypocalcemia (p=0.008; r=0.899) and metabolic acidosis (p=0.032; r=0.814). CONCLUSIONS Testing urinary trypsinogen-2 in patients with AP is rapid and useful. Patients over the age of 65 with hypoxia, metabolic acidosis and hypocalcemia tend to present a prolonged average hospital stay and higher mortality.