Screening studies of a population in primary health care are sparsely reported. The aim was to describe observed atypical behaviours that may be associated with autism spectrum conditions, in a population (n = 4329) of infants at eight months. Observations were performed by paediatric nurses. An observational instrument, named SEEK developed for child health care, was used focusing on social interaction, communication, motor skills, and an interview with parents. The analysis contains descriptive statistics, correlation analysis and a logistic regression model (cut-point 8 SEEK points). Infants scoring 8 points or more were observed a second time by psychologists and judged to be in the risk zone for atypical development. Delayed reaction to stimuli and preverbal language development were significant atypical behaviours together with deficits in communication skills, the latter more often among boys than girls. However, 7% scored 4 points or more indicating minor developmental problems. Catching early signs are crucial for both proactive care and intervention. © 2015 Taylor & Francis.