Background The study purpose was to assess the relationship between affective temperaments and procrastination and to examine the role of emotional reactivity as a mediator in this relationship. We hypothesized that depressive, cyclothymic, irritable and anxious temperaments as well as emotional reactivity would be positively correlated with procrastination while the hyperthymic temperament would be negatively correlated, and that emotional reactivity would mediate the relationship between affective temperaments and procrastination. Participants and procedure The sample consisted of 315 healthy Caucasian adults (193 women and 122 men) aged 18-69 (M = 31.64, SD = 12.14). The Polish version of the Temperament Evaluation of Memphis, Pisa, Paris and San Diego Auto-Questionnaire (TEMPS-A) was used to assess affective temperaments (depressive, cyclothymic, hyperthymic, irritable and anxious). The temperament traits postulated by the regulative theory of temperament were measured with the Formal Characteristics of Behaviour – Temperament Inventory Revised (FCB-TIR). Procrastination was evaluated via a Polish version of the Pure Procrastination Scale (PPS). Results The affective temperaments positively correlated with procrastination, except for hyperthymic temperament (negative correlation). Emotional reactivity and perseveration had a positive relationship with procrastination, while briskness, endurance and rhythmicity had a negative correlation. Cyclothymic temperament and emotional reactivity were found to be significant predictors of procrastination; hyperthymic temperament, endurance and rhythmicity may provide buffers against procrastination. Conclusions Cyclothymic temperament is an important predictor of procrastination. Emotional reactivity significantly mediated between cyclothymic temperament and procrastination. Hyperthymic temperament, endurance and rhythmicity may provide a buffer against procrastination.