Background: Snakebite is a global health issue and treatment with antivenom continues to be problematic. Brown snakes(genus Pseudonaja) are the most medically important group of Australian snakes and there is controversy over the dose ofbrown snake antivenom. We aimed to investigate the clinical and laboratory features of definite brown snake (Pseudonajaspp.) envenoming, and determine the dose of antivenom required.Methods and Finding: This was a prospective observational study of definite brown snake envenoming from the AustralianSnakebite Project (ASP) based on snake identification or specific enzyme immunoassay for Pseudonaja venom. From January2004 to January 2012 there were 149 definite brown snake bites [median age 42y (2–81y); 100 males]. Systemic envenomingoccurred in 136 (88%) cases. All envenomed patients developed venom induced consumption coagulopathy (VICC), withcomplete VICC in 109 (80%) and partial VICC in 27 (20%). Systemic symptoms occurred in 61 (45%) and mild neurotoxicity in2 (1%). Myotoxicity did not occur. Severe envenoming occurred in 51 patients (38%) and was characterised by collapse orhypotension (37), thrombotic microangiopathy (15), major haemorrhage (5), cardiac arrest (7) and death (6). The medianpeak venom concentration in 118 envenomed patients was 1.6 ng/mL (Range: 0.15–210 ng/mL). The median initialantivenom dose was 2 vials (Range: 1–40) in 128 patients receiving antivenom. There was no difference in INR recovery orclinical outcome between patients receiving one or more than one vial of antivenom. Free venom was not detected in 112/115 patients post-antivenom with only low concentrations (0.4 to 0.9 ng/ml) in three patients.Conclusions: Envenoming by brown snakes causes VICC and over a third of patients had serious complications includingmajor haemorrhage, collapse and microangiopathy. The results of this study support accumulating evidence that givingmore than one vial of antivenom is unnecessary in brown snake envenoming.