Hypothesis: Laparoscopy has become a popular approach for the surgical treatment of benign and even malignant colorectal diseases. Several authors have reported better preserved immunity in patients undergoing laparoscopic compared with conventional colorectal surgery. The present study addresses the hypothesis that specific and nonspecific immunity are differently affected by laparoscopic and conventional colorectal surgery. Design: Nonrandomized control trial. Setting: University hospital. Patients: Seventy prospectively enrolled patients with colorectal diseases undergoing laparoscopic (n=35) or open (n=35) surgery. Main Outcome Measures: Blood samples were taken prior to surgery as well as on days 1, 3, and 5 after surgery. Cell numbers of lymphocyte subpopulations as well as natural killer cells were determined by flow cytometry, and interleukin 6 and C-reactive protein serum levels were measured. Results: Significant differences between study and control patients (P≤.05) were detected regarding circulating interleukin 6 and C-reactive protein levels with a reduced proinflammatory response to surgery in patients after laparoscopic surgery. Furthermore, postoperative natural killer cell counts were significantly higher in patients after laparoscopic surgery. The levels of B lymphocytes and T lymphocytes and helper T-cell counts and cytotoxic (suppressor) T-cell counts did not show significant differences after open or laparoscopic surgery. Conclusions: Our findings indicate a less pronounced proinflammatory response to surgical trauma in patients after minimally invasive surgery. The nonspecific immune response appears to be less affected by laparoscopic surgery when compared with open surgery while the specific cell-mediated immunity is equally affected. These findings are important because a divergent effect on specific and nonspecific immunity of laparoscopic surgery for colorectal disease has not been reported before.