The purpose of this study was to investigate whether platelet-rich plasma therapy for early knee osteoarthritis is associated with good clinical outcomes and a change in magnetic resonance imaging (MRI) structural appearances. The design was a prospective cohort study following patients 1 year after platelet-rich plasma therapy for knee osteoarthritis. Twenty-two patients were treated with platelet-rich plasma for early osteoarthritis, confirmed with a baseline MRI. Inclusion criteria were Kellgren grade 0-II with knee pain in patients aged 30 to 70 years. All the patients received a 6-mL platelet-rich plasma injection using the Cascade system. Fifteen subjects underwent clinical assessments at baseline, 1 week, and 1, 3, 6, and 12 months, and MRIs at 1 year. Pain scores significantly decreased, whereas functional and clinical scores increased at 6 months and 1 year from baseline. Qualitative MRIs demonstrated no change per compartment in at least 73% of cases at 1 year.