Clinical practice guidelines are important for transmitting research findings into practice and facilitating the application of evidence-based practice (EBP). There is a paucity of knowledge about the impact of guideline implementation strategies in primary care physical therapy. The aim of this study was to evaluate the effect of a guideline implementation intervention in primary care physical therapy in western Sweden. An implementation strategy based on theory and current evidence was developed. A tailored, multi-component implementation intervention, addressing earlier identified determinants, was carried out in three areas comprising 28 physical therapy practices including 277 physical therapists (PTs) (intervention group). In two adjacent areas, 171 PTs at 32 practices received no intervention (control group). The core component of the intervention was an implementation seminar with group discussions. Among other components were a website and email reminders. Data were collected at baseline and follow-up with a web-based questionnaire. Primary outcomes were the self-reported awareness of, knowledge of, access to, and use of guidelines. Secondary outcomes were self-reported attitudes toward EBP and guidelines. Analyses were performed using Pearsons χ2 test and approximative z-test. 168 PTs (60.6%) in the intervention group and 88 PTs (51.5%) in the control group responded to the follow-up questionnaire. 186/277 PTs (67.1%) participated in the implementation seminars, of which 97 (52.2%) responded. The proportions of PTs reporting awareness of (absolute difference in change 20.6%, p = 0.023), knowledge where to find (20.4%, p = 0.007), access to (21.7%, p < 0.001), and frequent use of (9.5%, NS) guidelines increased more in the intervention group than in the control group. The proportion of PTs reporting frequent guideline use after participation in the implementation seminar was 15.2% (p = 0.043) higher than the proportion in the control group. A higher proportion considered EBP helpful in decision making (p = 0.018). There were no other significant differences in secondary outcomes. A tailored, theory- and evidence-informed, multi-component intervention for the implementation of clinical practice guidelines had a modest, positive effect on awareness of, knowledge of, access to, and use of guidelines, among PTs in primary care in western Sweden. In general, attitudes to EBP and guidelines were not affected.