Objective: To estimate the size of men who have sex with men (MSM) in Chongqing municipality.
Methods: A community based investigation was conducted in Chongqing to estimate the number of personal social network (c value) in the general population through the network scale-up method (NSUM). All the participants were selected by multistage sampling randomly. Factors as c value, the number of acquaintance of MSM and its respective coefficient were used to estimate and adjust the size of MSM in Chongqing.
Results: The average size of personal social network for Chongqing residents was 330, with differences among place (P < 0.001), sex (P < 0.0001), age (P < 0.0001), education level (P < 0.0001). The size of social network changed into 310 after the adjustment on demography, back estimation and elimination of the outliers. The estimated population size for MSM was 16 767 after the adjustment according to the respective levels, with 95%CI from 14 602 to 18 932, which accounted for 0.21% of the total number of males, aged from 15 to 49 in Chongqing municipality.
Conclusion: NSUM was a new method for estimation of population size, which seemed worthy in promoting the practice of NSUM for its efficiency.