Another case of eosinophilic cystitis is reported. Special interest is placed in the incorrectly assigned nature of this disease entity. Most of the authors tend to subdivide eosinophilic cystitis into two subtypes with its own clinical, histological, and evolutive aspects: allergic eosinophilic cystitis (AEC) and eosinophilic cystitis (EC). Several hypotheses have been put forward to explain its origin which, however, remains unclear. There is no specific treatment and its course tends to develop towards chronicity, with periods of remission and unpredictable exacerbation that warrant continuous monitoring. Diagnosis is by anatomopathological findings and differential diagnosis is warranted to distinguish it from bladder neoplasm (with which it is invariable confused), tuberculosis, etc.