Recently, we experienced two advanced gastric cancer (AGC) patients younger than 17 years of age. The first case was a 15-year, 2-month-old male who had suffered from epigastric soreness for 5 weeks. His grandfather died of gastric cancer at 39 years of age. Under the diagnosis of AGC, he underwent a total gastrectomy with D2 lymph node dissection. There was no evidence of distant metastasis. Pathologic examination revealed a 4.5×4 cm, signet ring cell adenocarcinoma with subserosal invasion and with metastasis in 9 of 42 regional lymph nodes (T2bN2M0). The second case was a 17-year, 11-month-old male who had suffered from epigastric pain for 2 years without familial clustering. Under the diagnosis of AGC, he underwent a distal subtotal gastrectomy with D2 lymph node dissection. There was no evidence of distant metastasis. Pathologic examination revealed a 3×2 cm, signet ring cell adenocarcinoma with subserosal invasion and with metastasis in 9 of 45 regional lymph nodes (T2bN2M0). The two patients have been alive without recurrence for 27 months and 4 months, respectively. Even among teenagers, patients with abdominal complaints should be subjected to a thorough examination of the gastrointestinal tract.