Objectives The purpose of the present study was to evaluate the association between self-perception of body weight, weight loss approaches and measured body mass index (BMI) and waist circumference (WC) among Sri Lankan adults. Methods A nationally representative sample of 600 adults aged =18 years was selected using a multi-stage random cluster sampling technique. An interviewer-administrated questionnaire was used to assess demographic characteristics, body weight perception, abdominal obesity perception and details of weight losing practices. Weight, height and waist circumference (WC) were measured and Asian anthropometric cut-offs for BMI and WC were applied. Results Body weight mis-perception was common among Sri Lankan adults. Two-thirds of overweight males and 44.7% females considered themselves as 'about right weight', moreover, 4.1% and 7.6% overweight men and women reported themselves as being 'underweight'. Over one third of both male and female obese subjects perceived themselves as 'about right weight' or 'underweight'. Nearly 32% of centrally obese men and women perceived that their WC is about right. People who perceived themselves as overweight or very overweight (n = 154) only 63.6% tried to lose weight (n = 98), and one quarter of adults sought advice from professionals (n = 39). Conclusion Body weight misperception was common among underweight, healthy weight, overweight, and obese adults in Sri Lanka. Over 2/3 of overweight and 1/3 of obese Sri Lankan adults believe they are in right weight category or are under weight.