Background: The pathophysiological basis of constipation is still unclear, and the role of colonic dysfunction is debated, especially in irritable bowel syndrome. Objective data are quite scarce, especially concerning colonic propulsive activity. Aims: To evaluate high- and low-amplitude colonic propulsive activity in constipated patients (slow-transit type and irritable bowel syndrome) in comparison with normal controls. Patients and Methods: Forty-five constipated patients (35 with slow-transit constipation and 10 with constipation-predominant irritable bowel syndrome) were recruited, and their data compared to those of 18 healthy subjects. Twenty-four-hour colonic manometric recordings were obtained in the three groups of subjects, and data concerning high- and low-amplitude colonic propulsive activity were then compared. Results: High-amplitude propagated contractions were significantly (p < 0.05) decreased in patients with slow-transit constipation and constipation-predominant irritable bowel syndrome with respect to controls (1.5 ± 0.4, 3.7 ± 2, and 6 ± 1 events/subject/day, respectively). In slow-transit constipation, a significant decrease of contractions’ amplitude was also observed. Concerning low-amplitude propagated contractions, patients with slow-transit constipation had significantly less events with respect to patients with constipation-predominant irritable bowel syndrome (46 ± 7 vs. 87.4 ± 19, p = 0.015); no differences were found between patients with slow-transit constipation and controls and between patients with constipation-predominant irritable bowel syndrome and controls. All three groups displayed a significant increase of low-amplitude propagated contractions after meals (6.3 ± 2 vs. 18.2 ± 5 for controls, p < 0.005; 6.4 ± 1.4 vs. 16.3 ± 2.4 for slow-transit constipation, p < 0.005; 10.5 ± 3.2 vs. 32.6 ± 7 for constipation-predominant irritable bowel syndrome, p = 0.001). Conclusions: Low-amplitude propagated contractions may represent an important physiologic motor event in constipated patients, reducing the severity of constipation in patients with irritable bowel syndrome and preserving a residual colonic propulsive activity in patients with slow-transit constipation.