Introduction: Prostate cancer is the most prevalent non-cutaneous malignancy in men. Mucinous adenocarcinoma is a rare histological variant, accounting for less than 0.5% of cases. Its distinctive imaging and histopathological features present unique diagnostic challenges. Case presentation: A 57-year-old male presented with sexual dysfunction, painful ejaculation, and hematuria. Clinical examination revealed a markedly enlarged prostate. Imaging studies, including scrotal and transrectal ultrasound, computed tomography, and multiparametric magnetic resonance imaging (MRI), demonstrated a complex, multilobulated prostatic mass with fluid-fluid levels and imaging features suggestive of mucin accumulation. Prostate biopsy confirmed adenocarcinoma with predominant mucinous features, including trabecular and cribriform patterns, and an ISUP grade group 4, indicating an aggressive tumor. On MRI, mucinous adenocarcinoma typically appears as a multicystic lesion with high T2 signal intensity and minimal diffusion restriction, which may delay diagnosis. These imaging characteristics differ from those of conventional prostate adenocarcinoma and can mimic benign cystic lesions. Discussion: Histopathological diagnosis is often challenging due to the extracellular mucin content. While treatment generally follows standard protocols for high-grade prostate cancer, including surgery, radiotherapy, and hormonal therapy, the rarity of this variant leaves many questions regarding prognosis and optimal management unanswered. Conclusion: Awareness of the distinct imaging and histopathological features of mucinous adenocarcinoma is crucial for accurate diagnosis and appropriate management. Further research is needed to better understand its clinical behavior and to establish evidence-based treatment guidelines.