A quasi-experiment, longitudinal and prospective study, in 60 patients with shoulder impingement syndrome, assisted in the Rehabilitation Service of "José María Velasco Ibarra" Hospital, in Tena city, Ecuador, was carried out from August, 2014 to March, 2015, aimed at determining the effectiveness of magnetotherapy in them. The shoulder performance was evaluated with the Constant-Murley test that was applied before and after the treatment, and in the statistical processing of the information the results obtained by means of the percentage calculation were compared through the Stuart- Maxwell marginal homogeneity test, with 95% of confidence. In the series the female sex (63.3%), the age group of 60 years and over (41.8%) and the subacromial bursal synovitis (46.6%) prevailed as main cause of the disorder. The quick clinical course of the patients demonstrated the effectiveness of the magnetotherapy, reason why its use is recommended in these cases. [ABSTRACT FROM AUTHOR]