The incidence of deep vein thrombosis (DVT) has been related to a number of risk factors, including genetic and acquired prothrombotic conditions, infections, inflammatory diseases, hematologic disorders, trauma, and drug use. Dehydration is a known independent risk factor for the development of thrombosis; however possibly insufficient evidence to form a strong association. The purpose of this case report is to present a 30-year-old male with DVT provoked by acute gastroenteritis-induced dehydration. The patient presented to the emergency department (ED) with a recent history of watery diarrhea for four days, for which he was diagnosed with gastroenteritis and managed at an outpatient care facility. The patient visited the ED again with a complaint of a one-day history of progressively worsening continuous pain in his left lower calf associated with swelling. The ultrasound-Doppler/duplex scan for the left lower limb venous system showed negative augmentation signs and non-compressibility of the deep venous system with partial occlusion/echogenic thrombosis extending from the external iliac vein, saphenofemoral junction, superficial femoral vein, popliteal vein, anterior tibial vein, and posterior tibial artery vena comitans. The patient was diagnosed with acute extensive DVT (multiple emboli). Patient care (medical treatment plan/therapeutic anticoagulation) was started in the ED and continued in the Critical Care Unit for close monitoring and care for a couple of days, after which he was transferred to the ward and then discharged in stable condition. He was prescribed a three-month course of appropriate medication regimen. This rare case presentation is a reminder to emergency physicians that dehydration might induce DVT and all patients, regardless of age, diagnosis or comorbidities, should always be risk assessed upon presentation and discharge, and prophylaxis should be provided according to their risk profile.