Hydroxylamine (HA) has been independently involved in several tragic accidents, which incurred numerous fatalities and injuries. Following these incidents, adiabatic calorimetry and computational chemistry research was conducted, suggesting potential reaction pathways of HA decomposition, but the mechanism of HA behavior still has not been completely understood. In the present work, the thermal decomposition of hydroxylamine was studied via isothermal and isoperibolic calorimetric measurements in a glass and in a metal reactor, respectively. Identification of stable intermediates, like ammonia, nitrates. or nitrites during the course of the reaction did not provide any conclusive results. The calorimetric measurements presented here show condition-dependent endothermic and exothermic reaction steps that are consistent with previous findings of computational chemistry. These findings corroborate previously reported results, according to which the NH(2-) moiety may trigger reaction runaway.