Just over a quarter of children diagnosed with an autism spectrum disorder (ASD) present with self-injurious behaviour (SIB).
That was the headline finding reported by Gnakub Soke and colleagues  who surveyed the 8000+ children "in the Autism and Developmental Disabilities Monitoring (ADDM) Network during the 2000, 2006, and 2008 surveillance years." THE ADDM network, as some people might know, is one and the same network that comes up with the [estimated] prevalence of autism in the United States (see here) and so carries quite a lot of statistical and clinical clout when it comes to data production. The actual figure for SIB was 27% when taking all the various ADDM sites into consideration but, much like the estimated prevalence stats, "with some variation between sites."
SIB is a topic that has been discussed on this blog a few times before (see here and see here for example). It's not something that generally makes for polite dinner table conversation and not something that many people would say makes for 'good PR' when it comes to the public perception of autism. Nevertheless, these and other estimates of SIB in autism (including its persistence) are one of the more pressing issues for those that present with such behaviours given not only the damage and distress that SIB can do to a person but also the effect(s) on family and loved ones too.
"Clinicians should inquire about SIB during assessments of children with ASD." I think that sentence is taken as read in light of the coincidence of autism and SIB. More than that however I think many people would like to see a lot more research into the potential hows and whys of SIB  and what can be done to minimise such 'challenging behaviour'. Yes, such acts may in some way be communicative for some people on the autism spectrum (i.e. pain, discomfort, etc), and if so, the use of a 'chemical cosh' is likely to have repercussions for such possible communication attempts. But where such SIB acts place someone at risk of permanent physical injury and/or increase the likelihood of extremes such as the need for corrective surgery, I don't think many people would hold back with the idea of appropriate management for such extreme behaviours.
 Soke GN. et al. Brief Report: Prevalence of Self-injurious Behaviors among Children with Autism Spectrum Disorder-A Population-Based Study. J Autism Dev Disord. 2016 Aug 26.
 Yuan X. & Devine DP. The role of anxiety in vulnerability for self-injurious behaviour: studies in a rodent model. Behavioural Brain Research. 2016; 311: 201-209.
Soke GN, Rosenberg SA, Hamman RF, Fingerlin T, Robinson C, Carpenter L, Giarelli E, Lee LC, Wiggins LD, Durkin MS, & DiGuiseppi C (2016). Brief Report: Prevalence of Self-injurious Behaviors among Children with Autism Spectrum Disorder-A Population-Based Study. Journal of autism and developmental disorders PMID: 27565654