The fluidized bed combustion of a biomass residue (olive husk) common in the Mediterranean area was investigated in a bench-scale reactor. The focus of the study was the high propensity of this fuel to have bed agglomeration problems during combustion as a consequence of the high potassium content of the ash. Temperature and pressure profiles in the bed were followed as a function of time during steady combustion tests at different operating conditions. Bed defluidization characteristic times were measured and correlated to the fuel ash buildup on the bed sand particles. In addition, a diagnostic tool based on the measurement of the dynamic pressure signal inside the bed was tested for its ability to predict bed agglomeration. On the basis of SEM/EDX analysis of agglomerate samples discharged from the bed after defluidization had occurred, the mechanisms of fuel ash-bed particle interaction and agglomerate formation are discussed.