Giardia lamblia is a protozoan that results in the commonly diagnosed giardiasis. Due to its prevalence and incidence worldwide, it is essential to recognize the different presentations of giardiasis, routes of transmission, modalities of diagnosis, treatments, and complications. Diagnostic modalities have evolved over the years and can be achieved reliably through noninvasive stool testing. Endoscopic duodenal aspirate and biopsies can also be used; however, they yield lower sensitivity and specificity rates and are therefore not used as a first-line modality for diagnosing giardiasis. Nonetheless, its use should be considered in cases with high suspicion and unremarkable stool testing. Herein, we discuss the case of a 27-year-old male with chronic weight loss and abdominal pain for six months diagnosed with G. lamblia through a duodenal biopsy.