To investigate which clinical, laboratory, and CT findings potentially facilitate the differential diagnosis between tubo-ovarian abscess (TOA) and periappendicular abscess (PAA), we retrospectively reviewed abdominal CT examinations and medical records for all women who presented to our medical center with unilateral right pelvic abscess formation who underwent CT evaluation from 2004-2014. A wide spectrum of clinical data and imaging findings were recorded. CT diagnoses were made in consensus by two experienced body radiologists blinded to the final diagnosis. Findings associated with the infections were compared using the chi-square (χ(2)) or the Fisher exact test. Ninety-one patients were included; 58 with PAA (mean age 46 years) and 33 with TOA (mean age 37 years). Pain on cervical motion (67 %) and vaginal discharge (21 %) were significantly more common in TOA; other clinical signs were similar. The presence of right ovarian vein entering the mass on CT had 100 % specificity and 94 % sensitivity to TOA. Distended right fallopian tube (79 %), mass posterior to mesovarium (76 %), contralateral pelvic fat stranding (55 %), and thickening of sacrouterine ligaments (55 %) were significantly more common in TOA. Positive "arrowhead sign" (91 %), mesenteric lymphadenopathy (85 %), small bowel wall thickening (55 %), fluid in the right paracolic gutter (50 %), and cecal wall thickening (48 %) were significantly more common in PAA;internal gas was revealed only in PAA (33 %). Distinct CT features can increase diagnostic certainty regarding the origin of right lower quadrant abscess in women.