Objectives: Ultrasonography, mammography and clinical examination (conventional triple assessment modalities) are compared to the gold standard of pathological size to assess their accuracy in measuring size of palpable breast cancer lesions. This knowledge has an important role in the patient's further management: for staging, choice of surgical technique and prognostication.Patients and methods: 71 tumours were studied in 70 patients who were prospectively collected over a 2 year period. Pearson's correlation test and Bland-Altman's plot were used to analyse tumour size by clinical palpation, ultrasound and mammogram.Results: Histopathological examination revealed 60 invasive carcinomas (58 ductal type, 2 lobular type), 4 ductal carcinoma in situ, 2 mixed and 5 special types. The pathological size varied from 0.5cm to 9.5cm. Ultrasound had the best correlation with pathological size, with r= 0.845 (p< 0.001), but with a tendency to underestimate. Size correlation for mammogram and clinical palpation were similar and statistically significant. However, the standard deviation of mammographic size was more compared to size on clinical examination (1.3 (mammogram) vs. 2.2 (clinical)). Clinical palpation was inclined to overestimate, whereas mammogram neither over-nor under-estimated size. Measurements using ultrasonography produced the lowest standard deviation, thus a lower variability from the mean. Conclusion:This study demonstrated that ultrasound is the more accurate modality compared to mammogram and clinical palpation size for the measurement of palpable breast cancer lesions. However, ultrasound may downstage tumours due to its tendency to underestimate size.