OBJECTIVE To educate primary health care professionals about the diagnosis and treatment of postobstructive diuresis (POD), a rare but potentially lethal complication associated with the relief of urinary obstructions. METHODS The main concepts and clinical evidence reviewed in this article were derived from a literature search of PubMed and Google Scholar. Expert opinion was used to supplement recommendations in areas with little evidence. RESULTS Urinary retention is a frequently encountered presentation seen by all physicians. Most family physicians are comfortable treating these patients, initiating investigations, and organizing appropriate follow-up. This article reviews a rare but potentially lethal complication known as POD. Postobstructive diuresis is a polyuric response initiated by the kidneys after the relief of a substantial bladder outlet obstruction. In severe cases this condition can become pathologic, resulting in dehydration, electrolyte imbalances, and death if not adequately treated. Primary care physicians should be familiar with this potential clinical entity, especially as they are generally the first to encounter and treat these patients. CONCLUSIONS Physicians aware of POD will be able to identify patients at risk and arrange the appropriate monitoring after relieving a urinary obstruction. Early diagnosis and treatment of pathologic POD will prevent mortality.