Health visitors need competences to promote healthy early parent-infant relationships. The aims of this study were to explore whether there are differences between groups of health visitors with and without additional parenting program education in terms of their knowledge of infant-parent interaction and their observation and assessment skills of such interactions. The cross-sectional study included 36 health visitors' certified Marte Meo therapists and 85 health visitors without additional parenting program education. Health visitors' observation skills were measured assessing five video-recorded mother-infant interactions. A questionnaire was used to measure their intention, self-efficacy, and knowledge. More certified Marte Meo therapists than health visitors without additional parenting program education reported a significantly higher mean level of knowledge of the early relationship, 6.42 (95% CI; 6.18-6.66) versus 5.05 (95% CI; 4.86-6.10), p = .04; and more certified Marte Meo therapists than health visitors without additional parenting program education reported a higher mean level of knowledge of infant self-regulation, 2.44 (95% CI; 2.18-2.71) versus 1.83 (95% CI; 1.62-2.03), p < .001. In the latter group, 54% (95% CI; 0.43-0.64) reported a significantly higher need for further education versus 22% (95% CI; 0.11-0.39), p = .001. Compared to health visitors without any parenting program education, health visitors certified as Marte Meo therapists reported a significantly higher frequency of correct assessment of mothers' sensitivity in two of five video-recordings, with 77.78% (95% CI; 0.61-0.87) compared to 45.88% (95% CI; 0.35-0.57) in Video 3, p = .001, and 69.44% (95% CI; 0.52-0.82) compared to 49.41% (95% CI; 0.39-0.60) in Video 4, p =.04, respectively. The results of the present study support the use of video-based education of health visitors to increase their knowledge of and skills in assessing parent-infant interactions. Randomized controlled trials are needed to determine whether the improved level of health visitors' knowledge and observation skills may be assigned to participation in the Marte Meo education program.