Our aim was to evaluate the effectiveness of tumour necrosis factor (TNF) inhibitors as add-on therapy for knee synovitis that did not respond to disease-modifying antirheumatic drugs (DMARDs) and other standard treatments in patients with peripheral spondyloarthritis (SpA). We retrospectively studied 27 SpA patients, in whom an anti-TNF agent was added for active peripheral arthritis with knee synovitis refractory to DMARDs and treatment with low-dose oral corticosteroids and/or nonsteroidal anti-inflammatory drugs (NSAIDs) and intra-articular (IA) corticosteroids. As response of knee synovitis, were considered the absence of swelling, tenderness, and decreased range of movement in the clinical examination, after 4 months of anti-TNF therapy. In twenty-four (88.9%) of the patients there was response of knee synovitis. No statistical differences in gender ( ), age ( ), disease subtype ( ), and pattern of arthritis ( ) between knee synovitis responders and nonresponders were found. Fourteen patients managed to stop DMARD therapy and six, all of whom were initially on DMARDs combination, to decrease the number of DMARDs to one, maintaining simultaneously the response of knee synovitis. Our results imply a beneficial effect of adjunctive anti-TNF therapy on knee synovitis not responding to DMARDs and other standard treatments in patients with peripheral SpA.