Unauthorized building works (UBWs), particularly those attached to external wallsof buildings, have posed serious threats to the safety of the community in Hong Kong. Asestimated by the government, there exist around 0.75 million UBWs in some 39,000private buildings throughout the territory. In spite of the plenteous literature on this topic,associated empirical studies have been relatively rare, and this is not constructive for theexploration of the causes of UBW proliferation. To straddle the existing research gap,this study empirically explores what types of unauthorized appendages dominate andwhat factors affect the degree of proliferation of unauthorized appendages in multi-storeyresidential buildings in Hong Kong. Given that the majority of Hong Kong's populacelive in this type of housing, residents and the general public are prone to UBW hazards intheir environments. Therefore, an empirical study like this one is necessary for providingvaluable insights to public administrators for making more informed decisions. Throughappraising 429 multi-storey residential buildings in Yau Tsim Mong, the Eastern Districtand Kowloon City, a profile of unauthorized appendages in these buildings wereobtained. The analysis results indicated that over 98 percent of these appendages were notconstructed purportedly for increasing usable floor space, but for enhancing the amenitiesenjoyed by the residents. Besides, building age, development scale and managementcharacteristics have a strong bearing on the number of unauthorized appendages presentin a building. These findings have far-reaching implications on the formulation ofgovernment policies regarding building safety in Hong Kong.