To evaluate the incidence of ecchymosis combined with postinflammatory hyperpigmentation (ECPH) over the course of 10 sessions of acupuncture therapy and to examine associated factors.An observational study was conducted from March 7, 2017 through March 6, 2018. This study included a total of 167 subjects and 326 bodily locations where acupuncture needles had been inserted. A 1-page questionnaire that included 14 items was used to collect patient data. The information collected was used to determine the incidence of ECPH. Chi-square tests were used to observe the associations between ECPH and demographic characteristics, dermatologic features, acupuncture-related factors, and other associated factors. Cox proportional hazards regression models were applied to calculate hazard ratios for ECPH among subjects treated with various frequencies of acupuncture and needles that differed in diameter.Although 186 subjects were initially enrolled, the study ultimately included 167 subjects and 326 bodily locations at which acupuncture needles were inserted. Over 10 sessions of acupuncture, ECPH was observed in 117 (70.06%, 117/167) subjects and 221 (67.79%, 221/326) bodily locations. Factors found to be associated with ECPH included: frequency of acupuncture, diameter of acupuncture needle, total number of acupuncture sessions, and bodily location at which acupuncture was administered (P < .05). Among subjects who received >2 acupuncture sessions per week, a higher frequency of acupuncture was associated with increased incidence of ECPH. Thicker acupuncture needle diameter was associated with a higher incidence of ECPH.The incidence of acupuncture-associated ECPH among the subjects included in the study was high. There were significant associations between ECPH and higher frequency of acupuncture as well as thicker diameter of acupuncture needles. Additional studies are required to confirm the findings.Trial registration number: AMCTR-OOC-17000109.