This study showed that nowadays, relatively shorter pen needles compared with those previously used are recommended for subcutaneous insulin therapy. Currently, the available shortest pen needles for subcutaneous injections is 4 mm in length, each. Even when the shortest pen needle is used, the risk for intramuscular injection during subcutaneous injection is 50% in boys aged 6–8 years, while it is 25% in those aged 9–12 years and 13–17 years for each. It is 25% in all the three age groups among the girls. Smaller pen needles can help to achieve more accurate subcutaneous injections.