Knee effusion in paediatric age group is usually due to hemarthrosis following an injury. However, there are several non-traumatic causes of knee effusion found in the paediatric age group. Evaluation and treatment for non-traumatic effusion in knee requires special attention. This is desired basically to differentiate between infectious, post-infectious, rheumatologic, hematologic, vasculitis and malignant diseases. Despite knee swelling prevailing in ~27% of general population, there is lack of consensus on diagnosis and management of this condition among Indians. The present case highlights the importance of a definite diagnostic pyramid and multidisciplinary approach required for early diagnosis and treatment of non-traumatic knee effusion in an adolescent with underlying juvenile spondyloarthropathy.