AIM The aim of this study was to compare thermal detection and pain thresholds in children with Down syndrome with those of their siblings.METHOD Sensory detection and pain thresholds were assessed in children with Down syndrome and their siblings using quantitative testing methods. Parental questionnaires addressing developmental age, pain coping, pain behaviour, and chronic pain were also utilized.RESULTS Forty-two children with Down syndrome (mean age 12y 10mo) and 24 siblings (mean age 15y) participated in this observational study. The different sensory tests proved feasible in 13 to 29 (33-88%) of the children with Down syndrome. These children were less sensitive to cold and warmth than their siblings, but only when measured with a reaction time-dependent method, and not with a reaction time-independent method. Children with Down syndrome were more sensitive to heat pain, and only 6 (14%) of them were able to adequately self-report pain, compared with 22 (92%) of siblings (p<0.001).INTERPRETATION Children with Down syndrome will remain dependent on pain assessment by proxy, since self-reporting is not adequate. Parents believe that their children with Down syndrome are less sensitive to pain than their siblings, but this was not confirmed by quantitative sensory testing.As early as 1887, John L Down made the following observation about persons with what we now call Down syndrome: 'common sensation is generally less acute than in ordinary persons. Pain is borne with wonderful callousness.' 1 More than a century later, a study reported that around 30% of parents of children with Down syndrome have difficulty perceiving whether or not their child is in pain, and that 70% of parents have difficulty identifying the location of their child's pain. 2 These results were confirmed in a prospective study among a group of individuals with Down syndrome and a comparison group. The individuals with Down syndrome had more problems locating a painful stimulus and also reacted to the painful stimulus later than did the individuals in the comparison group. 3 Defrin et al. 4 applied quantitative sensory testing to assess the heat pain sensitivity of 11 adults with Down syndrome and 14 adults without Down syndrome, and concluded that those with Down syndrome were more sensitive to heat pain than those without (p=0.06). The ultimate goal of quantitative sensory testing is to better understand the mechanisms involved in pain transduction, transmission, and perception under normal and pathophysiological conditions. 5 Different techniques have been developed to assess mechanical, thermal, current perception, and pain thresholds. 5 Using these techniques, particularly low pain thresholds were found in children with functional abdominal (visceral) pain or with musculoskeletal pain, 6 and sensory deficits were identified in individuals with neuropathic pain, 7 to name a few examples. Down syndrome is the primary cause of congenital intellectual disability worldwide. More than 80 different associated anomalies have been identified i...