Objective: To compare tumor growth, intraperitoneal implantation, and abdominal wall metastasis after laparotomy and CO2 pneumoperitoneum in a rat ovarian cancer model. Methods: To mimic intraoperative rupture of an ovarian tumor in a syngenic rat ovarian carcinoma model, 105 malignant cells were injected intraperitoneally after a 5-cm vertical midline laparotomy or after the insufflation of a CO2 pneumoperitoneum achieved with 4 mmHg or 10 mmHg intra-abdominal pressure. Two weeks later, the intraperitoneal tumor growth and the tumor dissemination were evaluated semiquantitatively with a scoring system. The scores attributed to each organ were added to calculate the dissemination score of each animal. Results: The mean (± SD) dissemination score was 83.4 ± 12 in the laparotomy group and 67.3 ± 16 and 71.9 ± 17 in the 4 and 10 mmHg CO2 pneumoperitoneum groups, respectively (P < .01). The scores for the peritoneum were 21.8 ± 3.8 in the 10 mmHg pneumoperitoneum group and 18 ± 2.4 in the laparotomy group (P < .01). In the laparotomy group, the implant found along the midline scar accounted for a mean of 62.6 ± 15% of the peritoneal score, whereas the trocar site metastases did not influence the peritoneal score in the pneumoperitoneum groups. The incidence of wound metastasis was 96% in the laparotomy group and 55% and 54% in the 4 mmHg and 10 mmHg pneumoperitoneum groups, respectively. Conclusion: In this model, tumor growth was greater after laparotomy than after laparoscopy, but peritoneal tumor dissemination was more severe after CO2 pneumoperitoneum.