Purpose This study aims to compare the performance of contrast-enhanced computed tomography (CeCT) and 18 F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) in detecting small tumor implants and metastatic lymph nodes (LNs) in the abdominopelvic cavity in patients with colorectal cancer. Methods We enrolled 16 patients who were clinically suspected of experiencing a recurrence (6 male, 10 female; mean age $61{pm}14$ years). All subjects underwent CeCT and PET/CT, and the performance of these methods was compared with regard to detecting recurrences. The final diagnosis of a recurrence was made clinically. Results CeCT identified 38 lesions in 12 patients, all of which were detected by PET/CT. PET/CT found 27 additional lesions in 8 patients, comprising 9 seeding nodules (2 in the right upper quadrant of the abdomen and 7 in the pelvic cavity) and 18 LNs (2 celiac, 2 paraaortic, 2 hepatic hilar, 11 common iliac, 1 external iliac). Most additional lesions were located in the pelvic cavity (approximately 78% of seeding nodules and 67% of lymph nodes). The maximum standardized uptake value (SUVmax) of the additional seeding nodules that were detected solely by PET/CT was significantly higher compared with the CeCT- and PET/CT-confirmed nodules ($5.5{pm}4.2$ vs. $2.9{pm}2.5$, p=0.03). The seeding nodules that were detected only by PET/CT were significantly smaller than the CeCT- and PET/CT-confirmed nodules (long axis: $1.0{pm}0.3$ cm vs. $2.0{pm}1.1$ cm, p=0.001; short axis: $0.8{pm}0.3$ cm vs. $1.4{pm}0.8$ cm, p=0.004; mean of both axes: $0.9{pm}0.3$ cm vs. $1.7{pm}0.9$ cm, p=0.001). Similarly, PET/CT-only-detected LNs were significantly smaller than CeCT- and PET/CT-identified LNs ($0.7{pm}0.1$ cm vs. $2.3{pm}1.2$ cm, p<0.0001). Conclusion PET/CT is superior to CeCT in detecting seeding nodules and metastatic LNs in patients with recurrent colorectal cancer. Specifically, PET/CT detects subcentimeter lesions in anatomically deformed pelvic cavities.