Pharmaceutical compositions are provided comprising one or more orally deliverable dose units, each comprising a selective cyclooxygenase-2 inhibitory compound of low water solubility in a therapeutically effective amount, wherein the compound is present in the form of solid particles, about 25% to 100% by weight of which are smaller than 1 micrometer. The compositions are useful in treatment or prophylaxis of cyclooxygenase-2 mediated conditions and disorders and have particular advantages where rapid onset of therapeutic effect is desired. The novel Form I and Form II crystalline forms of celecoxib are described. The crystalline forms have unique chemical and physical properties relative to other solid state forms of celecoxib and are characterized by their powder x-ray diffraction (PXRD) patterns, differential scanning calorimetric (DSC) thermograms, and other physical characterizations.