Pediatric Collections offers what you need to know – original, focused research in a snapshot approach. While infections are common, and most are mild and easily diagnosed, the first part of this 2-part series on infectious diseases, "Part 1: Can't Miss Diagnoses," includes cases with diagnoses that may be deadly and are challenging to recognize. Many of the presentations herein are seemingly benign and could easily be dismissed at first glance, and some are initially concerning but are without an obvious diagnosis. However, if these diagnoses are missed, there is a risk of serious morbidity or death and/or significant public health implications. These are the initial presentations that keep us up at night and run through our heads in clinic and at the bedside. They are the diagnoses we don't want to miss. Are you missing something? Are you letting a case report walk out the door? It is our goal that after reading these cases, you will be more alert and open to the idea of unusual and potentially dangerous cases walking into your practice.