Substance abuse and sexual ill health often go hand in hand. Despite this, no previous studies have investigated whether, and if so how, young people’s sexuality is given meaning in child welfare assessments due to suspected substance abuse. To investigate this, 15 child welfare workers in Sweden were recruited for a semi-structured interview through a strategic selection. The interviews were examined with the support of thematic analysis, which resulted in an overarching theme showing a lack of an area of knowledge. The social workers stated that they had not been trained in SRHR during their basic training or through further training in the roles as child welfare workers. However, this did not mean that they dismissed sexual health matters, rather that they developed individual approaches to face such questions. A common and recurring motto was “to not investigate more than necessary”, which meant that social workers often focused on risk and vulnerability in relation to substance use and related life conditions, and they also related to other areas of knowledge such as violence and crime. The social workers often referred to young persons’ right to confidentiality and privacy when it came to talking about positive aspects of young people’s sexuality, which meant that young people were rarely given space to talk about possible lustful connections between substance use and their sexuality. Overall, the lack of an area of knowledge within the child welfare services illuminates a need for targeted educational efforts toward child welfare professionals, efforts that are in line with the Swedish national strategy regarding sexual and reproductive health and rights for all.